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Microsoft QuickBASIC: Learning to Use Microsoft QuickBASIC ════════════════════════════════════════════════════════════════════════════ Microsoft(R) QuickBASIC: Learning to Use Microsoft QuickBASIC For IBM(R) Personal Computers and Compatibles ════════════════════════════════════════════════════════════════════════════ Information in this document is subject to change without notice and does not represent a commitment on the part of Microsoft Corporation. The software described in this document is furnished under a license agreement or nondisclosure agreement. The software may be used or copied only in accordance with the terms of the agreement. It is against the law to copy the software on any medium except as specifically allowed in the license or nondisclosure agreement. No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose without the express written permission of Microsoft. (C)Copyright Microsoft Corporation, 1988. All rights reserved. Simultaneously published in the U.S. and Canada. Printed and bound in the United States of America. Microsoft, MS, MS-DOS, CodeView, and GW-BASIC are registered trademarks of Microsoft Corporation. IBM is a registered trademark of International Business Machines Corporation. Intel is a registered trademark of Intel Corporation. Lotus and 1-2-3 are registered trademarks of Lotus Development Corporation. WordStar is a registered trademark of MicroPro International Corporation. ──────────────────────────────────────────────────────────────────────────── Contents Introduction Instant Feedback Instant Help Hardware Requirements The QuickBASIC Package Printed Documentation On-Line Documentation Document Conventions Requesting Assistance PART 1 GETTING STARTED Chapter 1 Setting Up Microsoft(R) QuickBASIC The Setup Program The Setup Main Menu Installation QB Express Getting Into QuickBASIC If You Are a Novice Programmer If You Already Know BASIC If You Use a Mouse Chapter 2 Using Menus and Commands Starting QuickBASIC The QuickBASIC Environment The Menu Bar The Reference Bar Opening Menus QuickBASIC's On-Line Help Using On-Line Help The Help Menu Choosing Commands Using Dialog Boxes Anatomy of a Dialog Box Displaying a Dialog Box Other Dialog-Box Features Issuing Commands Directly Shortcut Keys for Commands Other Key Combinations Exiting from QuickBASIC For More Information Chapter 3 QuickBASIC's Windows Windows Available with Easy Menus The View Window Loading Programs in the View Window Moving the Cursor Scrolling Text Starting a New Program Changing Window Sizes QuickBASIC's Other Windows Moving between Windows Executing Code in the Immediate Window Monitoring Variables with the Watch Window The Help Window Context-Sensitive Help Hyperlinks Exiting from QuickBASIC and Saving Programs For More Information Chapter 4 Interlude: BASIC for Beginners What is a Program? Comments Displaying Words and Numbers on the Screen Variables Storing Data in Memory Variable Types Integer Variables Floating-Point Variables String Variables Assigning Values to Variables Calculations Integer Division and the Remainder Operator Precedence of Operations Math Functions Expressions Displaying Variables and Expressions Entering Data with the INPUT Statement Arrays of Variables Declaring Arrays Specifying Array Elements Logical Relations Used in Decision-Making Relational Operators Boolean Expressions Compound Expressions Using Logical Statements to Control Program Flow Repeating Program Operations The FOR...NEXT Loop The DO...LOOP The DO WHILE Loop The DO UNTIL Loop Writing a Simple BASIC Program For More Information Books about BASIC Books about DOS PART 2 HANDS ON WITH QUICKBASIC Chapter 5 The QCARDS Program Building QCARDS Loading a Program When You Start QuickBASIC A Quick Tour of QCARDS The QCARDS Program Declarations and Definitions Comments Statements Following the END Statement Calling QCARDS Procedures from the Immediate Window Breaking an Unconditional Loop from QCARDS The Module-Level Code Structured Programming with Procedures A Profile of the Parts of the Program Defining a Procedure in QCARDS Saving Edited Text For More Information Chapter 6 Editing in the View Window The Smart Editor Automatic Formatting Syntax Checking Errors Detected When You Run Your Program Help for Error Messages Overtyping the Error Automatic Procedure Declarations Working with Selected Text Blocks Cutting or Copying Selected Text Pasting a Text Block Manipulating Selected Text Searching and Replacing Text Defining the Symbolic Constant Replacing Multiple Occurrences of Text Checking Your Work For More Information Chapter 7 Programming with On-Line Help Using On-Line Help to Construct Statements On-Line Help for Keywords Hyperlinks in On-Line Help On-Line Help for Program Symbols Printing Screens from On-Line Help For More Information Chapter 8 Using Example Code from On-Line Help Copying Example Code from On-Line Help Indenting a Block of Code Copying Large Code Blocks from On-Line Help Editing the Block Copied from On-Line Help Finishing the QCARDS Code Using QCARDS For More Information Chapter 9 Debugging While You Program Debugging Commands Debug-Menu Commands Debugging Commands on the Run Menu Function Keys Used in Debugging Debugging a Procedure Learning about Procedures Continuing a Suspended Program Isolating a Bug Closing the Watch Window Automatic Procedure Declarations Creating a Stand-Alone Executable File Learning about QuickBASIC's Other Menu Items For More Information PART 3 QUICKBASIC MENUS AND COMMANDS Chapter 10 Getting Around in QuickBASIC 10.1 Starting QuickBASIC 10.1.1 The QB Command 10.1.2 The /NOHI Option 10.1.3 The QuickBASIC Screen 10.2 Opening Menus and Choosing Commands 10.2.1 Keyboard Technique 10.2.2 Using Shortcut Keys 10.3 Using Dialog Boxes 10.4 Using Windows 10.4.1 Window Types 10.4.2 Splitting the View Window (Full Menus Only) 10.4.3 Changing the Active Window 10.4.4 Changing Window Size 10.4.5 Scrolling in the Active Window 10.5 Using the Immediate Window 10.5.1 Statements Not Allowed 10.5.2 Doing Calculations 10.5.3 Testing Screen Output 10.5.4 Invoking Procedures 10.5.5 Changing the Values of Variables 10.5.6 Simulating Run-Time Errors 10.6 Using the Watch Window 10.7 Using the Mouse 10.8 Using On-Line Help 10.8.1 Help Features 10.8.2 Hyperlinks 10.8.3 Moving in Help Windows 10.8.4 Help Files 10.8.5 Hard-Disk System 10.8.6 Removable-Disk System Chapter 11 The File Menu 11.1 New Program Command 11.2 Open Program Command 11.2.1 Specifying a File 11.2.2 Listing Directory Contents 11.3 The Merge Command (Full Menus Only) 11.4 Save Command (Full Menus Only) 11.5 Save As Command 11.6 Save All Command (Full Menus Only) 11.7 Create File Command (Full Menus Only) 11.8 Load File Command (Full Menus Only) 11.9 Unload File Command (Full Menus Only) 11.10 The Print Command 11.11 DOS Shell Command (Full Menus Only) 11.12 Exit Command Chapter 12 Using the Editor 12.1 Entering Text 12.2 Selecting Text 12.3 Indenting text 12.4 Using Placemarkers in Text 12.5 The Smart Editor 12.5.1 When Is the Smart Editor On? 12.5.2 Automatic Syntax Checking 12.5.3 Error Messages 12.5.4 Automatic Formatting 12.6 Entering Special Characters 12.7 Summary of Editing Commands Chapter 13 The Edit Menu 13.1 Understanding the Clipboard 13.2 Undo Command (Full Menus Only) 13.3 Cut Command 13.4 Copy Command 13.5 Paste Command 13.6 Clear Command (Full Menus Only) 13.7 New SUB Command (Full Menus Only) 13.7.1 Creating a New SUB Procedure 13.7.2 Default Data Types for Procedures 13.7.3 Changing a Procedure's Default Type 13.7.4 Saving and Naming Procedures 13.8 New FUNCTION Command (Full Menus Only) Chapter 14 The View Menu 14.1 SUBs Command 14.2 Next SUB Command (Full Menus Only) 14.3 Split Command (Full Menus Only) 14.4 Next Statement Command (Full Menus Only) 14.5 Output Screen Command 14.6 Included File Command (Full Menus Only) 14.6.1 Nesting Include Files 14.6.2 Finding Include Files 14.7 Included Lines Command Chapter 15 The Search Menu 15.1 Defining Target Text 15.2 Find Command 15.3 Selected Text Command (Full Menus Only) 15.4 Repeat Last Find Command (Full Menus Only) 15.5 Change Command 15.6 Label Command (Full Menus Only) Chapter 16 The Run Menu 16.1 Start Command 16.2 Restart Command 16.3 Continue Command 16.4 Modify COMMAND$ Command (Full Menus Only) 16.5 Make EXE File Command 16.5.1 Creating Executable Files 16.5.2 Quick Libraries and Executable Files 16.5.3 Types of Executable Files 16.5.3.1 Programs that Use the Run-Time Module 16.5.3.2 Stand-Alone Programs 16.5.4 Run-Time Error Checking in Executable Files 16.5.5 Floating-Point Arithmetic in Executable Files 16.6 Make Library Command (Full Menus Only) 16.6.1 Unloading and Loading Modules 16.6.2 Creating Libraries 16.7 Set Main Module Command (Full Menus Only) 16.7.1 Changing the Main Module 16.7.2 The .MAK File Chapter 17 Debugging Concepts and Procedures 17.1 Debugging with QuickBASIC 17.2 Preventing Bugs with QuickBASIC 17.3 QuickBASIC's Debugging Features 17.3.1 Tracing (Full Menus Only) 17.3.2 Breakpoints and Watchpoints 17.3.3 Watch Expressions 17.3.4 Watch Window 17.3.5 Immediate Window 17.3.6 Other Debugging Features Chapter 18 The Debug Menu 18.1 Add Watch Command 18.2 Instant Watch Command 18.3 Watchpoint Command (Full Menus Only) 18.4 Delete Watch Command 18.5 Delete All Watch Command (Full Menus Only) 18.6 Trace On Command (Full Menus Only) 18.7 History On Command (Full Menus Only) 18.7.1 History Back 18.7.2 History Forward 18.8 Toggle Breakpoint Command 18.9 Clear All Breakpoints Command 18.10 Break on Errors Command (Full Menus Only) 18.11 Set Next Statement Command Chapter 19 The Calls Menu (Full Menus Only) 19.1 Using the Calls Menu 19.2 Active Procedures Chapter 20 The Options Menu 20.1 Display Command 20.2 Set Paths Command 20.3 Right Mouse Command (Full Menus Only) 20.4 Syntax Checking Command(Full Menus Only) 20.5 Full Menus Command Chapter 21 The Help Menu 21.1 Index Command 21.2 Contents Command 21.3 Topic Command 21.4 Help On Help Command Glossary Figures Figure 2.1 QuickBASIC Invocation Screen Figure 2.2 The File Menu Figure 2.3 Help Dialog Box for the Help Menu Figure 2.4 Open Program Dialog Box Figure 2.5 Display Dialog Box Figure 2.6 Help on Output Screen Command Figure 3.1 Windows Available with Easy Menus Figure 3.2 Open Program Dialog Box Figure 3.3 Output Screen for Code Lines Figure 3.4 Immediate Window Showing Lines Just Entered Figure 3.5 Placing Variables in the Watch Window Figure 3.6 QuickSCREEN for PRINT Statement Figure 3.7 Example Screen for PRINT Statement Figure 3.8 Save As Dialog Box Figure 4.1 Addresses in Memory Figure 4.2 Array Created by the BASIC Statement DIM Price (4) Figure 5.1 QCARDS' Interface Figure 5.2 Modules and Procedures Figure 5.3 SUBs Dialog Box Figure 5.4 Save As Dialog Box Figure 6.1 Error-Message Dialog Box Figure 6.2 Error Message Figure 6.3 Help on Error Message Figure 6.4 Find Dialog Box Figure 6.5 Change Dialog Box Figure 6.6 Change, Skip, Cancel Dialog Box Figure 7.1 QuickSCREEN for IF...THEN...ELSE Statement Figure 7.2 Symbol Help for CardNum Figure 7.3 Instant Watch Dialog Box Figure 7.4 Print Dialog Box (Help) Figure 8.1 Example Screen for DO...LOOP Statement Figure 8.2 QuickSCREEN for SELECT CASE Statement Figure 8.3 Code Showing Call to AsciiKey Procedure Figure 9.1 Selecting the SELECT CASE Choice$ Block Figure 9.2 DirectionKey Procedure in View Window Figure 9.3 Restart Program Error Message Figure 9.4 Setting a Breakpoint Figure 9.5 Symbol Help for Symbolic Constant HOME Figure 9.6 Error in Naming Symbolic Constant for the ENV Key Figure 9.7 Make EXE File Dialog Box Figure 10.1 Top Half of QuickBASIC Invocation Screen Figure 10.2 Bottom Half of QuickBASIC Invocation Screen Figure 10.3 The File Menu Figure 10.4 Load File Dialog Box Figure 10.5 Display Dialog Box Figure 10.6 QuickBASIC Screen with Five Windows Open Figure 10.7 Immediate Window Figure 10.8 Simulated Run-Time Error Figure 10.9 Watch Window Figure 10.10 Help on the PRINT Statement Figure 10.11 Dialog Box for Missing Help File Figure 11.1 Open Program Dialog Box Figure 11.2 Merge Dialog Box Figure 11.3 Save Dialog Box Figure 11.4 Create File Dialog Box Figure 11.5 Load File Dialog Box Figure 11.6 Unload File Dialog Box Figure 11.7 Print Dialog Box Figure 11.8 Exit Dialog Box Figure 12.1 Syntax Error Message Figure 12.2 Initial Help Screen on the OPEN Keyword Figure 13.1 New SUB Dialog Box Figure 13.2 New FUNCTION Dialog Box Figure 14.1 New SUBs Dialog Box Figure 14.2 Move Dialog Box Figure 15.1 Find Dialog Box Figure 15.2 Change Dialog Box Figure 15.3 Change, Skip, Cancel Dialog Box Figure 15.4 Label Dialog Box Figure 16.1 Modify COMMAND$ Dialog Box Figure 16.2 Make EXE File Dialog Box Figure 16.3 Make Library Dialog Box Figure 16.4 Set Main Module DIalog Box Figure 18.1 Add Watch Dialog Box Figure 18.2 Instant Watch Dialog Box Figure 18.3 Watchpoint Dialog Box Figure 18.4 Delete Watch Dialog Box Figure 19.1 Sequence of Procedures on Calls Menu Figure 20.1 Display Dialog Box Figure 20.2 Set Paths Dialog Box Figure 20.3 Right Mouse Dialog Box Figure 21.1 Index Entries for Help Figure 21.2 Table of Contents for Help Figure 21.3 Help on the FOR...NEXT Statement Figure 21.4 Help on Help Screen Tables Table 10.1 QuickBASIC Shortcut Keys Table 10.2 Scrolling Table 10.3 Mouse Commands Table 10.4 Help Keys Table 12.1 QuickBASIC Indentation Controls Table 12.2 Editing Commands Table 15.1 Search Options Table 15.2 Search Restrictions Table 17.1 Additional Debugging Features QCARDS Code Entries QCARDS Code Entry 1 QCARDS Code Entry 2 QCARDS Code Entry 3 QCARDS Code Entry 4 QCARDS Code Entry 5 QCARDS Code Entry 6 QCARDS Code Entry 7 QCARDS Code Entry 8 QCARDS Code Entry 9 QCARDS Code Entry 10 QCARDS Code Entry 11 Optional QCARDS Code Entry 1 Optional QCARDS Code Entry 2 Optional QCARDS Code Entry 3 QCARDS Code Entry 12 QCARDS Code Entry 13 QCARDS Code Entry 14 QCARDS Code Entry 15 QCARDS Code Entry 16 QCARDS Code Entry 17 QCARDS Code Entry 18 QCARDS Code Entry 19 QCARDS Code Entry 20 QCARDS Code Entry 21 QCARDS Code Entry 22 Optional QCARDS Code Entry 4 QCARDS Code Entry 23 QCARDS Code Entry 24 QCARDS Code Entry 25 QCARDS Code Entry 26 QCARDS Code Entry 27 QCARDS Code Entry 28 QCARDS Code Entry 29 QCARDS Code Entry 30 ──────────────────────────────────────────────────────────────────────────── Introduction Microsoft(R) QuickBASIC is a programming environment that includes all the tools you need for writing, editing, running, and debugging programs. These tools are integrated with a powerful version of the BASIC programming language and an on-line help system that explains everything about both the environment and the language. Instant Feedback Microsoft QuickBASIC speeds your programming and learning by giving virtually instant feedback for your ideas. When you write a program, you enter "code" (sequences of QuickBASIC statements) that describe what you want the program to do. QuickBASIC checks the validity of each line as you enter it, then immediately translates your code into a form the computer can execute. If your code contains errors that make it impossible to translate, QuickBASIC specifies the error and helps you correct it. As soon as your code is correct, you can press a key and immediately run it. If your code doesn't run as you expect, you can use QuickBASIC's sophisticated debugging tools to track and correct flaws in your code's logic.You get the speed and power of a compiled language without the tedious cycles of separate editing, compiling, running, and debugging. Instant Help Microsoft QuickBASIC's on-line help system includes two parts. The Microsoft QB Advisor contains explanations and runnable examples of every statement in the QuickBASIC language. Also, you can get on-line help for every aspect of the QuickBASIC environment, all symbols you define in your program, and error messages. In this manual you will see how to get information on the following with on-line help: ■ QuickBASIC statements and functions ■ Menu and dialog-box items and options ■ Special keys and key combinations for editing and debugging ■ How to correct errors in your program ■ Symbols you define in your programs Hardware Requirements Microsoft QuickBASIC requires an IBM Personal Computer or IBM(R)-PC compatible with at least 384 kilobytes (K) of available memory and a minimum of 720K disk-drive capacity. A hard disk and 640K of memory are recommended for best performance. The QuickBASIC environment fully supports any mouse that is compatible with the Microsoft Mouse. See Section 10.7 for complete information on using your mouse with QuickBASIC. ────────────────────────────────────────────────────────────────────────── NOTE Throughout this manual, the term "DOS" refers to both the MS-DOS(R) and IBM Personal Computer DOS operating systems. The name of a specific operating system is used when it is necessary to note features that are unique to that system. ────────────────────────────────────────────────────────────────────────── The QuickBASIC Package The Microsoft QuickBASIC package includes two manuals, an extensive on-line help system, example programs, and other on-line documentation. The next sections describe the contents of the package. Printed Documentation Your Microsoft QuickBASIC package includes two manuals. This manual discusses the QuickBASIC programming environment. The first two parts are a tutorial on how to use QuickBASIC. The last part is a reference on QuickBASIC menus and commands. The following list describes these parts in more detail: Part Content ────────────────────────────────────────────────────────────────────────── "Getting Started" General description of how to use QuickBASIC and a brief introduction to BASIC programming. "Hands On with Tutorial introduction to the Easy-Menus version QuickBASIC" of the QuickBASIC environment. The tutorial gives you practice with editing, debugging, and on-line help and guides you in creating your first QuickBASIC application, QCARDS.BAS. "QuickBASIC Menus and Reference to the QuickBASIC environment that Commands" presents detailed information on each command on QuickBASIC's Full Menus. Full Menus provide the complete multiple-module functionality of QuickBASIC. Use this section to extend your knowledge after you feel comfortable with the fundamentals of QuickBASIC. "Glossary" Definitions of terms used in the documentation. ────────────────────────────────────────────────────────────────────────── This manual provides the following information that you'll need to begin programming with QuickBASIC: ■ The QuickBASIC environment ■ The QuickBASIC implementation of the BASIC language ■ The principles of programming If you are new to programming, new to the BASIC language, or both, you will need to learn the environment, the QuickBASIC version of the BASIC language, and general programming skills. You should begin with Chapters 1-4 in Part 1, "Getting Started." If you already know how to program in BASIC, you should be able to get right to programming after reading Chapters 1-3 in Part 1. In the tutorial in Part 2, "Hands On with QuickBASIC," you will practice using some of the QuickBASIC environment's most exciting features. You'll use the sophisticated editor, on-line help, and debugging features. When you finish the tutorial, you will have built a useful database application program, QCARDS.BAS. The QuickBASIC package includes another manual, Programming in BASIC, which discusses the following: ■ Specific, practical programming topics, each illustrated by extensive programming examples ■ The action and syntax of each QuickBASIC statement and function with tables listing the statements and functions by task groups ■ Information on topics such as converting interpreted BASIC programs to run in QuickBASIC, changes in Version 4.5 from previous versions of QuickBASIC, and compiling and linking from DOS Use Programming in BASIC for in-depth information on programming topics and a synopsis of the BASIC language. On-Line Documentation Microsoft QuickBASIC includes comprehensive on-line help and several disk files that provide supplementary information and programming examples. These are described in the following list: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Documentation Purpose ────────────────────────────────────────────────────────────────────────── On-Line Help All information needed for programming in QuickBASIC. When you use help commands within the environment, QuickBASIC searches several files to provide the information. The file QB45QCK.HLP includes summaries and syntax descriptions of each QuickBASIC statement and function. The file QB45ADVR.HLP contains comprehensive information on using each statement Documentation Purpose ────────────────────────────────────────────────────────────────────────── comprehensive information on using each statement and function, including example code you can copy and run. The file QB45ENER.HLP has explanations of all environment menus, commands, dialog boxes, and error messages. README.DOC A file describing changes to QuickBASIC that occurred after the manuals were printed. PACKING.LST A file describing each file on the QuickBASIC distribution disks. LEARN.COM Microsoft QB Express, a computer-based training program that gives an overview of QuickBASIC. Sample programs All the programs from Programming in BASIC. Check the file called PACKING.LST to locate them. Other sample programs are also included. Many demonstrate advanced programming techniques and Documentation Purpose ────────────────────────────────────────────────────────────────────────── demonstrate advanced programming techniques and algorithms. ────────────────────────────────────────────────────────────────────────── Document Conventions This manual uses the following document conventions: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Example of Convention Description ────────────────────────────────────────────────────────────────────────── QB.LIB, ADD.EXE, COPY, Uppercase (capital) letters indicate file names LINK, /X and DOS-level commands. Uppercase is also used for command-line options (unless the application accepts only lowercase). SUB, IF, LOOP, PRINT, Bold capital letters indicate language-specific Example of Convention Description ────────────────────────────────────────────────────────────────────────── SUB, IF, LOOP, PRINT, Bold capital letters indicate language-specific WHILE, TIME$ keywords with special meaning to Microsoft BASIC. Keywords are a required part of statement syntax, unless they are enclosed in double brackets as explained below. In programs you write, you must enter keywords exactly as shown. However, you can use uppercase letters or lowercase letters. CALL Proc(arg1!, var2%) This kind of type is used for program examples, program output, words you should type in, and error messages within the text. CONST FALSE = 0 A column of three dots indicates that part of the . example program has been intentionally omitted. . . CHAIN "PROG1" END Example of Convention Description ────────────────────────────────────────────────────────────────────────── ' Make one pass The apostrophe (single right quotation mark) marks the beginning of a comment in sample programs. filespec Italic letters indicate placeholders for information, such as a file name, that you must supply. Italics are also occasionally used in the text for emphasis. [[optional-item]] Items inside double square brackets are optional. ALT+F1 Capital letters are used for the names of keys and key sequences, such as ENTER and CTRL+R. A plus (+) indicates a combination of keys. For example, CTRL+E means to hold down the CTRL key while pressing the E key. Example of Convention Description ────────────────────────────────────────────────────────────────────────── The carriage-return key, sometimes marked with a bent arrow, is referred to as ENTER. The cursor movement ("arrow") keys on the numeric keypad are called DIRECTION keys. Individual DIRECTION keys are referred to by the direction of the arrow on the key top (LEFT, RIGHT, UP, DOWN) or the name on the key top (PGUP, PGDN). The key names used in this manual correspond to the names on the IBM Personal Computer keys. Other machines may use different names. "defined term" Quotation marks usually indicate a new term defined in the text. Video Graphics Array Acronyms are usually spelled out the first time (VGA) they are used. Example of Convention Description ────────────────────────────────────────────────────────────────────────── (VGA) they are used. ────────────────────────────────────────────────────────────────────────── The following syntax block shows how some of these document conventions are used in this manual: GET[[#]] filenumber [[,[[recordnumber]][[,variable]]]] . . . PUT[[#]] filenumber [[,[[recordnumber]][[,variable]]]] Requesting Assistance If you feel you have discovered a problem in the software, please report the problem using the Product Assistance Request form at the back of this manual. If you have comments or suggestions regarding any of the manuals accompanying this product, please use the Documentation Feedback form at the back of this manual. ──────────────────────────────────────────────────────────────────────────── PART 1 GETTING STARTED ──────────────────────────────────────────────────────────────────────────── Part 1, "Getting Started," introduces you to the Microsoft QuickBASIC environment, then moves on to an introductory discussion on BASIC programming. Each major feature of the environment is explained, then demonstrated in a brief hands-on exercise. Each chapter ends with a section specifying where you can look for more information on each of the topics discussed. Chapter 1 guides you through installation of QuickBASIC, using the SETUP program provided. Chapters 2 and 3 introduce you to working with QuickBASIC's Easy Menus, dialog boxes, and windows. Chapter 4 introduces the BASIC language for novice programmers. Be sure you understand everything in this chapter before moving ahead. If you have programmed in another language this chapter should provide all you need to complete Part 2, "Hands On with QuickBASIC," and start using QuickBASIC to write your own programs. If you are new to programming, you may want to consult some of the books on BASIC listed at the end of the chapter. ──────────────────────────────────────────────────────────────────────────── Chapter 1 Setting Up Microsoft(R) QuickBASIC Your Microsoft QuickBASIC package includes the file SETUP.EXE (on the Setup/Microsoft QB Express disk). This program automates installation of QuickBASIC, and lets you choose display options to install or update files required by QuickBASIC and your hardware. This chapter discusses ■ Installing Microsoft QuickBASIC ■ Using Microsoft QB Express ■ Exploring QuickBASIC, depending on your experience level The Setup Program If you do not have a hard disk, be sure you have five formatted, 360K removable disks (or an equivalent amount of space on disks of other sizes). If you have a hard disk, you need 1.8 megabytes of space available to install all QuickBASIC files. To start SETUP Place the Setup/Microsoft QB Express disk in your disk drive, and type setup at the DOS prompt. Each screen in the SETUP program contains the following: ■ An explanation of the current screen or the following screen. ■ The Setup menu, which you use to choose what you want to do next. Generally, the Setup menu on each screen lets you continue, go back a screen, examine the options you've chosen, or return to the starting screen. To move within the menu and make choices, use the DIRECTION keys, then press ENTER when your choice is highlighted. ■ A prompt at the bottom of the screen tells you how to move on to the next step. ────────────────────────────────────────────────────────────────────────── NOTE If you make a mistake when installing QuickBASIC with SETUP, you can go back to any previous point and start again from there. You can run SETUP as many times as you like. ────────────────────────────────────────────────────────────────────────── The Setup Main Menu The items on the Setup Main menu allow you to choose the defaults for all options (Easy Setup) and customize the options you choose during setup (Full Setup). If you are a novice programmer, you should choose Easy Setup. As you learn more about QuickBASIC, you can reset these options from within the environment without running SETUP again. If you are an experienced programmer, Full Setup lets you tailor the appearance and certain behaviors of QuickBASIC. Chapter 20, "The Options Menu," describes how QuickBASIC handles the search paths and colors you choose during setup. (They correspond to the Options menu's Display and Set Paths commands.) Whether you choose Easy or Full Setup, use the Show Options menu command to look at the final settings before completing the installation. Installation After you have decided about options, choose Perform Installation from the menu to begin automated installation. QuickBASIC prompts you for each disk you need to insert in your disk drive as installation progresses. If you have a hard disk, QuickBASIC places the files you need in the directories specified in either the Easy Setup or Full Setup options. If the directories don't already exist, QuickBASIC creates the directories you specify on your hard disk. If you do not have a hard disk, you must start the installation phase with five formatted removable disks. QuickBASIC prompts you when to install each disk. You might want to label the disks, using the same names as appear on the original disks. QB Express After installation is complete, return to the Main Setup menu. Even if you've used QuickBASIC before, you should choose Exit and Run QB Express from the main menu. Microsoft QB Express, a brief computer-based training program, introduces the QuickBASIC environment and gives you some practice in the things you'll do when you fire up QuickBASIC itself. If you've used QuickBASIC before, QB Express alerts you to Version 4.5 enhancements to the environment. Getting Into QuickBASIC QuickBASIC is a superb environment in which to learn programming, but it is not specifically designed as a "learn to program" environment. QuickBASIC provides all the tools you need for programming──editing, debugging, and on-line help──plus a powerful version of the BASIC language. Chapters 2-9 of this book are a tutorial on QuickBASIC. A typewriter icon marks all the practice exercises. If You Are a Novice Programmer In learning to use QuickBASIC, you need to distinguish between the tools provided by the environment, and the language itself. The best way to acquaint yourself with the environment is by reading Chapter 2, "Using Menus and Commands," and Chapter 3, "QuickBASIC's Windows." Then, try Chapter 4, "Interlude: BASIC for Beginners," which should give you enough perspective on BASIC programming to complete Part 2, "Hands On with QuickBASIC." Part 2, "Hands On with QuickBASIC," is a tutorial that introduces you to editing, using on-line help, and debugging in the context of an extended program example. In a series of exercises, you will complete the coding of QCARDS.BAS, a real application program. Each of these chapters takes one to two hours to complete. Although "Hands On with QuickBASIC" is not a tutorial on programming, QCARDS.BAS provides a good model of program structure. You can also use the code from QCARDS in other programs you write. But remember, the purpose of the QCARDS tutorial is to teach you quickly how to use the tools in the QuickBASIC environment. You don't have to understand all the programming techniques to type in the QCARDS code. To learn more about programming, read some of the BASIC programming texts listed at the end of Chapter 4, "Interlude: BASIC for Beginners." Programming in BASIC, included with this package, presents extended examples and explanations of selected programming topics. If You Already Know BASIC If you are already familiar with BASIC, you should be able to move quickly through Chapter 2, "Using Menus and Commands," and Chapter 3, "QuickBASIC's Windows," which teach the fundamentals of menus and windows, and opening, clearing, and saving files. You can skip Chapter 4 completely and move right to Part 2, "Hands On with QuickBASIC," to learn the use of QuickBASIC's advanced editing, on-line help, and debugging features. Even if you have used a previous version of QuickBASIC, you may find some new programming techniques in QCARDS.BAS, the example program you will build as you practice advanced environment features. The comments in the QCARDS code explain how the program works. If the comments do not provide enough information, the programming techniques are discussed in Programming in BASIC. If You Use a Mouse QuickBASIC fully supports pointing devices that are compatible with the Microsoft Mouse. See Section 10.7 for complete information on using QuickBASIC with a mouse. ──────────────────────────────────────────────────────────────────────────── Chapter 2 Using Menus and Commands This chapter teaches you how to start Microsoft QuickBASIC and use the Easy Menus. A "menu" is a list of commands. In QuickBASIC, you can choose between two sets of menus──Easy Menus and Full Menus. Easy Menus, which you'll work with here, contain all the commands a novice programmer needs to use QuickBASIC. Part 3, "QuickBASIC Menus and Commands" describes the advanced commands on the Full Menus. When you have completed this chapter, you'll know how to ■ Open and use menus and dialog boxes ■ Consult QuickBASIC's on-line help to answer questions ■ Use function keys and shortcut-key combinations This chapter will take one to one and one-half hours to complete. Starting QuickBASIC Start QuickBASIC now: 1. Type qb at the DOS prompt. The QuickBASIC screen appears. 2. Press ENTER to display essential information about the QuickBASIC environment. You can use PGUP and PGDN to move around in this text. 3. Press ESC to clear this information from the screen. ────────────────────────────────────────────────────────────────────────── NOTE If your computer has a monochrome or liquid-crystal display, or if you use a Color Graphics Adapter (CGA) with a black-and-white monitor, see Sections 10.1.1, "The QB Command," and 10.1.2, "The /NOHI Option," for additional QB invocation options. If you start QuickBASIC with the /nohi or /b /nohi option, what are referred to as high-intensity letters in this manual may have a different appearance. ────────────────────────────────────────────────────────────────────────── The QuickBASIC Environment QuickBASIC's programming tools are instantly available. They include features for program organization, editing, syntax checking, file management, printing, and debugging──even customizing the colors of the environment. The Menu Bar The menus on the menu bar at the top of the QuickBASIC screen contain the QuickBASIC environment commands (see Figure 2.1). You'll use them as you write and modify programs in the View window. Menu bar Title bar Scroll bars View window │ │ ││ │ File Edit View Search Run │Debug Options ││ │ Help ┌┬─────────────────┬────────────└ Untitled ───────┼┼────────────┼─────┤├── ││ New Program │ ││ │ ││ Open Program... │ ││ │ ││ Save As... │ ││ │├─────────────────┤ ││ ││ Print... │ │└─────────────────────── │├─────────────────┤ │ ││ Exit │ │ │└─────────────────┘ │ │ │ │ │ │ │ │ │ │ │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── │ │ │ F1=Help Removes│currently loaded program from memory CN 00001:001 │ │ └─┬─┘└───┬───┘ Reference bar Immediate CAPS LOCK and────────────┘ Row and window NUM LOCK indicators column indicator Figure 2.1 QuickBASIC Invocation Screen The Reference Bar The reference bar at the bottom of the screen tells which keys to press to perform important actions (see Figure 2.1). As you work on a program, the reference bar updates information about the environment and your program. When a command is highlighted, the reference bar briefly describes how to use the command. Row and column counters indicate where you are in your program, and CAPS LOCK and NUM LOCK indicators tell how your keyboard is set. Opening Menus You can execute most QuickBASIC commands by choosing them from the menus. When you press the ALT key, QuickBASIC highlights the file menu, and one letter in each menu name appears in high-intensity video. To open a menu, press the ALT key, then press the key corresponding to the high-intensity letter in the menu name. You can open the menus and move among them using the DIRECTION keys (the UP, DOWN, LEFT, and RIGHT arrow keys) . To open a menu 1. Press ALT to select the File menu. When you "select" (highlight) a menu, its name is shown in a reverse-video block. If you press ALT again, the menu name loses the highlight. 2. Press ENTER to open the File menu (see Figure 2.2). ┌───────┐ │ File │ ├───────┴──────────┐ │ New Program │ │ Open Program... │ │ Save As... │ ├──────────────────┤ │ Print... │ ├──────────────────┤ │ Exit │ └──────────────────┘ Figure 2.2 The File Menu ■ Press the UP or DOWN key to select successive commands in an open menu. ■ Press the RIGHT or LEFT key to open adjacent menus. 3. Press ESC to close the menu without executing a command. The cursor returns to the View window, the part of the screen where you edit your program. You can always back out of any situation by pressing ESC. QuickBASIC's On-Line Help If you need additional information about menus or other QuickBASIC features, consult on-line help. You can get help on BASIC keywords, the elements of the language, the QuickBASIC environment, and error messages. Using On-Line Help There are several ways to get on-line help in QuickBASIC. For help on menu names or commands, select the name or command, then press F1. If you want help on any part of a program, place the cursor within the word, then press F1. To move around in on-line help, do the following: ■ Press PGDN to see additional screens. ■ Press PGUP to move back through screens you have already seen. ■ Press ESC to cancel on-line help. If you need more information on using any on-line help function, hold down the SHIFT key while pressing F1 for a general description of on-line help. The Help Menu Most on-line help is available through the Help menu. Try this to use on-line help: 1. Press ALT to select the File menu without opening it. 2. Press LEFT to select the Help menu. 3. Press F1. On-line help displays the information shown in Figure 2.3 about the Help menu: ┌──────────────────────── HELP: Help Menu ─────────────────────┐ │ ┌───────────────────────────────────────────────────────────┐ │ │ │ Use the Help menu to display: │ │ │ │ ■ a list of BASIC language keywords │ │ │ │ ■ a list of general topics about QuickBASIC and the │ │ │ │ BASIC programming language │ │ │ │ ■ detailed, context-sensitive information on the │ │ │ │ program item shown in a topic cursor │ │ │ │ │ │ │ │ To use the Help menu commands now │ │ │ │ 1. Press ESC to return to the Help menu │ │ │ │ 2. Use the DIRECTION keys to select (highlight) a │ │ │ │ command │ │ │ │ 3. Press ENTER to execute the command │ │ │ └───────────────────────────────────────────────────────────┘ │ ├───────────────────────────────────────────────────────────────┤ │ < OK > │ └───────────────────────────────────────────────────────────────┘ Figure 2.3 Help Dialog Box for the Help Menu 4. Press ENTER when you finish reading the text. 5. Press DOWN to open the Help menu. You can get help with each of the items on the Help menu by moving the highlight among the commands with the DIRECTION keys, and pressing F1 for explanations. If there is no on-line help available for the current item, or if the necessary help file is unavailable, QuickBASIC either displays a message, beeps, or both. The Help menu has the following commands: Command Action ────────────────────────────────────────────────────────────────────────── Index Displays an alphabetical listing of all QuickBASIC keywords. Place the cursor on a keyword and press F1 to get help on that keyword. Contents Displays a visual outline of the on-line help's contents. For detailed information on any category listed, place the cursor on the category and press F1. Topic Displays help for any word at the cursor position. If there is a word at the cursor position, it appears in the Help menu following the Topic command. If there is no word at the cursor position, the Topic command is inactive. Help on Help Explains how to use on-line help. ────────────────────────────────────────────────────────────────────────── Choosing Commands To "choose" (execute) a command, select the command by pressing the UP or DOWN key, then press ENTER or the high-intensity letter in the command name. (If a command has no high-intensity letter, it is not currently available for you to use.) If a command is followed by three dots (...), a dialog box (description to follow) appears when you choose the command. Commands not followed by dots execute immediately when you choose them. To learn more about a command before choosing it, press F1 for on-line help. After you read the help information, press ESC to clear help, then press ENTER if you want to choose the command. Try the following steps: 1. Press ALT, then press O to select the Options menu. This key combination opens the Options menu. In this manual, combinations of keys are written as key names connected with a plus sign. The sequence above is usually shown as ALT+O. 2. Press DOWN until Full Menus is highlighted. 3. Press F1 to display on-line help while Full Menus is selected. 4. Press ESC to clear on-line help. 5. Press ENTER to turn off Full Menus if the bullet (■) is present. Press ESC to close the Options menu without executing any of its commands if Full Menus does not have a bullet. The Full Menus command is a "toggle." If it is on (that is, if it has a bullet), then choosing it turns it off. If it is off (no bullet), choosing it turns it on. 6. Press ALT+O to open the Options menu again. Make sure there is no bullet beside Full Menus, then press ESC to close the menu. You only need to use DIRECTION keys when you want help with a command. If you don't need help, just choose commands by pressing the letter corresponding to the high-intensity letter in the command name. Using Dialog Boxes A "dialog box" appears when you choose any menu command followed by three dots (...). QuickBASIC uses dialog boxes to prompt you for information it needs before executing a command. Dialog boxes also appear when you ■ Enter a line of code containing a syntax error ■ Run a program that contains an error ■ Choose the Help command button in a dialog box ■ Request help for a menu or menu command ■ Try to end a session without saving your work Anatomy of a Dialog Box Dialog boxes include several devices you can use to give QuickBASIC information (see Figure 2.4). ┌─Text box ┌─List boxes │ │ │ │ │ │ ┌───────────────┼────── Open Program ─────┼───────────────────┐ │ ┌┴─────────────────────────┼─────────────────┐ │ │ File Name: │*.bas │ │ │ │ └──────────────────────────┼─────────────────┘ │ │ │ │ │ C:\QB4.5\DEMO │ │ │ Files ┌──┴──┐Dirs/Drives │ │ ┌────────────────────────────────────┐ ┌───────────────┐ │ │ │ATEST.BAS REMLINE.BAS │ │┌──┐ │ │ │BL.BAS SORTDEMO.BAS │ │ ∙∙ ░ │ │ │DEMO1.BAS TEST.BAS │ │SOURCE ░ │ │ │DEMO2.BAS TORUS.BAS │ │[-A-] ░ │ │ │DEMO3.BAS VARHELP.BAS │ │[-B-] ░ │ │ │DEMO4.BAS VARHELPZ.BAS │ │[-C-] ░ │ │ │HISTOGRM.BAS │ │ ░ │ │ │QBFORMAT.BAS │ │ ░ │ │ │QCARDS.BAS │ │ │ │ └░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░┘ └───────────────┘ │ ├─────────────────────────────────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └──────────┼───────────────────┼───────────────────┼──────────┘ └────────┬──────────┴───────────────────┘ └Command buttons Figure 2.4 Open Program Dialog Box The following list explains how to use these devices: Device Description ────────────────────────────────────────────────────────────────────────── Text box Type text, such as a file name, here List box Select one item from a group of listed items Command button Use to confirm entries, get help, or escape from the dialog box ────────────────────────────────────────────────────────────────────────── Displaying a Dialog Box When you first open a dialog box, it contains "default" settings──the settings people use most often. After that, when you display a dialog box, it reflects the choices you made the last time the box was displayed. The angle brackets on the default command button appear in high intensity. When you press ENTER, the default command button is chosen. You can use ALT key combinations or TAB to move around in a dialog box. Follow these steps to open and examine the File menu's Open Program dialog box: 1. Press ESC to close the Options menu if it is still open. 2. Press ALT+F, then press O to choose the File menu's Open Program command. The Open Program dialog box (shown in Figure 2.4) appears. It lets you load programs from disk files into the View window. 3. Press F1 to choose the Help command button. A help dialog box opens on top of the Open Program dialog box. You can use DIRECTION keys to move through the help text. 4. Press ESC to clear the help dialog box and return the cursor to the Open Program dialog box. 5. Press ALT to turn on the high-intensity letters you can use in combination with the ALT key. 6. Press TAB to move the cursor into the Files list box. If there are numerous entries in the list box, you can move among them either by pressing DIRECTION keys or the initial letter of the item you wish to select. 7. Press TAB or ALT+D to move the cursor to the Dirs/Drives list box. 8. Press ESC to close the dialog box without opening a program. Other Dialog-Box Features Other dialog-box features include option buttons and check boxes. You'll use these features in the Options menu's Display dialog box (see Figure 2.5) to change options──such as screen colors, scroll bars, and the distance between tab stops──chosen when you installed QuickBASIC. ┌──Option buttons. │ Move between them ┌List boxes. │ with UP or DOWN key. │Select one item. │ │ │ ┌──────────────────────── Display ─────────────┼────────────────┐ │ │ ┌─────────────────────── Colors ─────────────├──────────────┐ │ │ │ │ Foreground │ Background │ │ │ │ │ ┌──┴──┐ │ │ │ │ │ ┌ ┌─────────┐ ┌─────────┐ │ │ │ │ │ │ (∙) 1. Normal Text │ Black │ Black │ │ │ │ │ │ │ White ░ │ White ░ │ │ └─┼─┼─┤ ( ) 2. Current Statement │ Gray ░ │ Gray ░ │ │ │ │ │ │ BrWhite ░ │ BrWhite ░ │ │ │ │ │ ( ) 3. Breakpoint Lines │ ░ │ ░ │ │ │ │ └ │ │ │ │ │ │ └─────────┘ └─────────┘ │ │ │ │ │ │ │ │ │ │ │ └───────────────────────────────────────────────────────────┘ │ │ │ │ ┌────────────────── Display Options ────────────────────────┐ │ ┌─┼─┼──[X] Scroll Bars Tab Stops: 8 │ │ │ │ └───────────────────────────────────────────────────────────┘ │ │ ├───────────────────────────────────────────────────────────────┤ │ │ < OK > < Cancel > < Help > │ │ └──────────┼──────────────────┼─────────────────────┼───────────┘ │ └───────────┬──────┴─────────────────────┘ │ └─Command buttons. └─Check box. Press Choose to confirm settings, SPACEBAR to set. get help, or escape. Figure 2.5 Display Dialog Box Option buttons are turned on if a bullet (■) appears within the parentheses. Only one option in each group of option buttons can be turned on at a time. An X within the brackets indicates that a check box is turned on. You can turn on as many check boxes as you like. To set options, do the following: 1. Press ALT+O, then press D to choose the Option menu's Display command. The Display dialog box (shown in Figure 2.5) appears. 2. Press ALT+T to move the cursor to the Tab Stops text box. Type a new number if you want to change the number of spaces between tab stops while you are editing. For programming, 4 is a good choice. 3. Press ALT+S to move the cursor to the Scroll Bars check box. Press SPACEBAR to put an X in an empty check box or remove the X if the box already has one. (Scroll bars, shown on Figure 2.1, are only useful if you have a mouse.) 4. Set the three types of foreground and background colors, as follows: a. Press ALT plus the highlighted number (1, 2, or 3) to select the option whose colors you want to change. b. Press TAB to move to the foreground and background test boxes and press UP or DOWN to select the colors. c. Repeat the previous process two steps to change the Current Statement and Breakpoint Lines options. 5. Press ENTER to choose the command, confirming any new choices you've just made, or press ESC to return all settings to what they were when the dialog box was first displayed. The Current Statement option determines the attributes of the currently executing line in a running program. The Breakpoint Lines option sets the color for lines at which you set breakpoints. Note that Breakpoint Lines and Current Statement colors show only when you have a program running. Issuing Commands Directly You can use shortcut keys and key combinations to issue commands directly without opening menus to choose items. Shortcut keys are available for many QuickBASIC tasks. Shortcut Keys for Commands If a command has a shortcut key, it is listed beside the command. For example, instead of opening the Edit menu and choosing the Cut, Copy, or Paste commands, you can use SHIFT+DEL, CTRL+INS, and SHIFT+INS instead. Other Key Combinations There are other special keys and key combinations. For example, SHIFT+F1 always displays help on help; and F1 displays on-line help for menu names and commands or any keyword or program symbol at the cursor. Other key combinations use function keys, keys on the numeric keypad like INS and DEL, and many combinations of the SHIFT, ALT, or CTRL keys with other keys. For example, you can use the RIGHT and LEFT keys to move the cursor right and left on the screen. To move the cursor to the next word beyond the current cursor position, hold down CTRL and press LEFT or RIGHT. Try this exercise to see how common shortcut keys and key combinations work: 1. Press ALT+V to open the View menu. The SUBs command is automatically selected. Note the shortcut key (F2) to the right of the command name. 2. Press DOWN to select the Output Screen command. Note that its shortcut key is F4. 3. Press F1 to consult on-line help for an explanation of Output Screen (see Figure 2.6). ┌────────────────── HELP: Output Screen Command ──────────────────┐ │ ┌──────────────────────────────────────────────────────────────┐ │ │ │ Use the Output Screen command to toggle between the │ │ │ │ QuickBASIC environment screen and the program output │ │ │ │ screen. │ │ │ │ │ │ │ │ This enables you to refer to the ouput previously │ │ │ │ generated by your program while you are editing or │ │ │ │ debugging it. │ │ │ │ │ │ │ │ Press F4 to toggle between screens with one keystroke. │ │ │ └──────────────────────────────────────────────────────────────┘ │ ├──────────────────────────────────────────────────────────────────┤ │ < OK > │ └──────────────────────────────────────────────────────────────────┘ Figure 2.6 Help on Output Screen Command 4. Press ENTER to close the help screen. ENTER is the shortcut key for the default (or currently selected) command button. 5. Press ESC to close the View menu. Exiting from QuickBASIC When you end a session, QuickBASIC checks to see if you have any unsaved work in progress. If you do, a dialog box asks if you want to save your work. Because you haven't entered any text in this session, press N if this dialog box appears when you do the following: Press ALT+F, then press X to choose the File menu's Exit command to return to DOS. If you made and confirmed changes in the Displays dialog box, they are saved in a file called QB.INI when you exit. They become the defaults the next time you start QuickBASIC. For More Information For more information on the topics covered in this chapter, see the following: Where to Look What You'll Find ────────────────────────────────────────────────────────────────────────── Section 10.1.1, "The QB Command," Explanations of QuickBASIC's and 10.1.2, "The /NOHI Option" invocation options Section 10.8, "Using On-Line Help," Complete description of on-line help and Chapter 21, "The Help Menu" Section 10.2, "Opening Menus and More information on menus and dialog Choosing Commands," and 10.3, boxes "Using Dialog Boxes" Section 10.2.2, "Using Shortcut A listing of the common shortcut keys Keys" Section 12.7, "Summary of Editing A complete list of key combinations Commands" used for editing ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 3 QuickBASIC's Windows In this chapter you will learn how to use Microsoft QuickBASIC's windows as you write a short program. You'll learn how to ■ Open an existing program and move the cursor ■ Activate, move between, and change the window size ■ Execute BASIC statements from the Immediate window ■ Monitor values of variables with the Watch window ■ Use the Help window ■ Save programs as files on disk This chapter takes about one to one and one-half hours to complete. Windows Available with Easy Menus QuickBASIC is called a "window-oriented" environment because the screen is divided into separate areas in which you can perform different tasks. Some windows, such as the View window and the Help window, display material loaded from disk files. Other windows, such as the Watch window, display information QuickBASIC has about the current program. With Easy Menus, the windows shown in Figure 3.1 are available. Watch window Help window │ │ │ File Edit View Search Run Debug Options │ Help └Untitled X = 10: 0 │ ┌────────────────────── HELP: CLS Statement QuickSCREEN ────────┼─────┤├── │ QuickSCREEN Details Example Contents Index │───────────────────────────────────────────────────────────────────────── │CLS - a device I/O statement that clears the display screen │ │Syntax │ CLS [{0|1|2}] │ │ = If all arguments are omitted, either the graphics viewport or the │ text viewport are cleared, depending upon previous uses of the VIEW │ statement. │ = 0 clears the screen of all text and graphics. │ = 1 clears only the graphics viewport, if it is active. │ = 2 clears only the text viewport, leaving the bottom screen line │ unchanged. ├──────────────────────────────── Untitled ───────────────────────────┤├── │CLS │ │ │ │ │ │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ─────────────────────│────────── │ │ │ │ <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> │ 00001:003 │ │ Immediate window View window Figure 3.1 Windows Available with Easy Menus Window Description ────────────────────────────────────────────────────────────────────────── View The window in which you do most of your programming. When you start QuickBASIC the View window is the "active window," the one containing the editing cursor. When you load a disk file, its contents appear in the View window. Immediate The window at the bottom of the screen. In it you can use single lines of BASIC code to test programming ideas and perform miscellaneous calculations. You can type in the Immediate window, but you cannot load disk files into it. Help A window that opens at the top of the screen when you press F1 or SHIFT+F1. Information about QuickBASIC keywords, symbols you define in your program, and using help is displayed in the Help window. Watch A window that opens at the top of the screen when you choose certain commands from the Debug menu. ────────────────────────────────────────────────────────────────────────── You can have several windows open at a time, but only one can be active at a time. By opening multiple windows, you can view different types of information simultaneously. For example, you can have program code in the View window, then display on-line help for the statement you want to use. The View Window The View window is where you do most of your programming. This section explains how to load an existing program from a disk file into the View window and move the cursor around in its text. Then you'll clear that program and write and run some lines of your own code. Loading Programs in the View Window When you load a file from a disk, its text appears in the View window. To load a program 1. Start QuickBASIC using the QB command you learned in Chapter 2. 2. Press ESC to clear the Welcome dialog box. 3. Press ALT+F, then press O to choose the File menu's Open Program command. QuickBASIC displays a dialog box like the one in Figure 3.2. Path-specification line Symbol Name gives path to files listed for next of next ┌─in Files list box. highest lowest │ ┌─directory ┌─directory │ ┌─Text box │ │ │ │ List boxes─┐ │ │ │ │ │ │ │ │ │ │ │ │ │ ┌───────────────┼────── Open Program ──┼──┼──────────────┼────┐ │ │ ┌┴──────────────────────┼──┼──────────────┼──┐ │ │ │ File Name: │ │ │ │ │ │ │ │ └───────────────────────┼──┼──────────────┼──┘ │ │ │ │ │ │ │ └─┼───C:\QB4.5\DEMO │ │ │ │ │ │ │ Dirs/Drives │ │ │ ┌───────────────────────────────────┴┐ │ ┌────────────┼──┐ │ │ │ATEST.BAS REMLINE.BAS ─┐ │ │ │┌──┐ │ │ │ │BL.BAS SORTDEMO.BAS │ │ └─┼ ∙∙ │ ░ │ │ │DEMO1.BAS TEST.BAS │ │ │SOURCE ─────┘ ░ │ │ │DEMO2.BAS TORUS.BAS │ │ │[-A-]─┐ ░ │ │ │DEMO3.BAS VARHELP.BAS ├────┐ │ │[-B-] ├─────┐ ░ │ │ │DEMO4.BAS VARHELPZ.BAS │ │ │ │[-C-]─┘ │ ░ │ │ │HISTOGRM.BAS │ │ │ │ │ ░ │ │ │QBFORMAT.BAS │ │ │ │ │ ░ │ │ │QCARDS.BAS ┘ │ │ │ │ │ │ └░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░│┘ └────────────┼──┘ │ ├─────────────────────────────────────┼──────────────────┼────┤ │ < OK > < Cancel > │ < Help > │ │ └─────────────────────────────────────┼──────────────────┼────┘ List box contains file names having ┘ Available drives┘ extension shown in text box Figure 3.2 Open Program Dialog Box The cursor is in the text box where *.bas is selected. Anything you type while *.bas is selected replaces it. The *.bas in the text box tells QuickBASIC to list all the files having that extension in the Files list box. This dialog box has the following features: Feature Function ────────────────────────────────────────────────────────────────────────── Text box Box for typing text, such as a file name Files list box Box that displays files in the directory specified on the path-specification line Dirs/Drives list box Box that shows the directories above and below the directory specified on the path-specification line and the drives available on your system ────────────────────────────────────────────────────────────────────────── The files in your list box should include QCARDS.BAS. To open it, type its name in the text box, or use the list box to select it, as described here: 1. Press TAB to move the cursor into the Files list box. 2. Press DIRECTION keys until the name of the program you want is selected. (Press SPACEBAR if the program you want is the first entry. ) 3. Select QCARDS.BAS. The name QCARDS.BAS replaces *.bas in the text box. 4. Press ENTER to load QCARDS.BAS in the View window. QCARDS is large (almost 40K), so it may take a few moments to load. When it is loaded, the name QCARDS.BAS appears in the View window's title bar. Moving the Cursor You can use the DIRECTION keys on the numeric keypad (the LEFT, RIGHT, UP, and DOWN arrow keys as well as HOME, END, PGUP, and PGDN) to move the cursor in a window. The DIRECTION keys move the cursor a single row or column at a time. HOME and END move the cursor to the first or last column of the current line. However, you can combine the CTRL key with DIRECTION keys to move the cursor in greater increments, as follows: Key Combination Cursor Movement ────────────────────────────────────────────────────────────────────────── CTRL+RIGHT Right one word CTRL+LEFT Left one word CTRL+HOME First line of current window CTRL+END Last line of current window ────────────────────────────────────────────────────────────────────────── Scrolling Text A window can contain far more text than is visible within its on-screen boundaries. "Scrolling" describes the movement of text into and out of the bounded screen area. You can scroll text using the following keys and combinations: Key Combination Scrolling Action ────────────────────────────────────────────────────────────────────────── PGUP Up by one whole screen PGDN Down by one whole screen CTRL+PGDN Right by one whole screen CTRL+PGUP Left by one whole screen ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── NOTE The CTRL+PGDN combination can be disorienting if you don't have text between columns 79-159. To confirm your place in a file, check the row and column counters in the lower right corner of the reference bar. You can press HOME to move the cursor to the first column of the current line. ────────────────────────────────────────────────────────────────────────── Starting a New Program When you load an existing program from disk, QuickBASIC clears everything else from memory before loading the program. In this section, you'll clear QCARDS.BAS from QuickBASIC's memory with the New Program command, then you'll type in a simple program. As you type in lines of code, notice that QuickBASIC capitalizes the keywords in the statements when you press ENTER. If you get an error message, press ESC to clear the message, then retype the line at the cursor. Follow these steps to clear QCARDS.BAS, then write and run some code: 1. Press ALT+F, then press N to choose the File menu's New Program command. 2. Type the following BASIC statements cls print "This is my first QuickBASIC program" print 2 + 2 3. Press ALT+R, then press S to choose the Run menu's Start command. If you typed everything correctly, QuickBASIC displays the program's output on the "output screen," which should look like the screen in Figure 3.3. ┌────────────────────────────────────────────────────────┐ │This is my first QuickBASIC program │ │ 4 │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ ┌─┤Press any key to continue │ │ └────────────────────────────────────────────────────────┘ └─Press a key to return to QuickBASIC environment. Figure 3.3 Output Screen for Code Lines In this program, CLS clears the screen, then the PRINT statement displays the quoted text in the upper left corner of the screen. Because PRINT can display the results of numeric expressions, the sum of the expression 2+2 appears on the next line. 4. Press a key to return to QuickBASIC's View window. 5. Press ALT+V, then press U to choose the View menu's Output Screen command to take another look at your program's results. 6. Press a key to return to QuickBASIC's View window. ────────────────────────────────────────────────────────────────────────── NOTE You can get help for any keywords you don't understand by placing the cursor on the keyword, then pressing F1. ────────────────────────────────────────────────────────────────────────── Changing Window Sizes You can easily increase or decrease the size of the windows on your screen. To increase the size of the active window, press ALT+PLUS once for each line you want to add. To reduce the size by one line, press ALT+MINUS. (Use the PLUS and MINUS keys on the numeric keypad.) To temporarily expand the active window to full screen, press CTRL+F10. You can restore the windows to their previous sizes by pressing this toggle again. The following steps illustrate this and prepare the windows for the exercise in the next section: 1. Press ALT+PLUS twice while the cursor is in the View window. This adds lines to the View window and compresses the Immediate window beneath it. 2. Press ALT+MINUS seven times to reduce the size of the View window. This decreases the number of lines in the View window while increasing the size of the Immediate window. 3. Press CTRL+F10 to expand the size of the current window temporarily to full-screen status. 4. Press CTRL+F10 again to restore the screen to its previous proportions. QuickBASIC's Other Windows When you start QuickBASIC and clear the opening dialog box, the View window contains the cursor, so it is the active window. Only one window can be active at a time. However, other windows are available. Note that the title bar of the active window is highlighted. Moving between Windows To move the cursor down one window, press the F6 key. To move the cursor up one window, press SHIFT+F6. If you have used CTRL+F10 to expand the current window, F6 and SHIFT+F6 still make the next and previous windows active. Executing Code in the Immediate Window The Immediate window at the bottom of the screen can be used as a utility window as you program in the View window. For example, if you want to clear the output screen, you can execute the CLS statement from the Immediate window. You can also use the Immediate window for doing calculations, or experimenting with programming ideas and previewing the results. When you exit from QuickBASIC, text in the Immediate window is lost. When you run lines of code in the View window, they are executed sequentially. In the Immediate window, a single line of code is executed whenever you put the cursor anywhere on that line, then press ENTER.You can type in either uppercase or lowercase in the Immediate window. Note that QuickBASIC doesn't capitalize keywords in the Immediate window as it does in the View window. Try the following procedure to execute lines of code in the Immediate window: 1. Press F6 to place the cursor in the Immediate window. 2. Type the following line: cls : print "This line comes from the Immediate window" This code consists of two BASIC statements separated by a colon. Separating statements with a colon allows you to put more than one statement on a line. 3. Press ENTER to execute the code on this line. QuickBASIC displays the output screen. 4. Press a key to return to the QuickBASIC environment. The cursor is placed on the next blank line in the Immediate window. 5. Type the following line, exactly as shown: CurrentTime$ = "" This defines a variable named CurrentTime$. The $ tells QuickBASIC it is a "string" variable (one consisting of a series of characters). The quotation marks have no space between them, so the string has a length of zero. 6. Press ENTER to execute this statement and assign the zero-length string to CurrentTime$. Next, you'll continue working in the Immediate window and use the BASIC TIME$ function to assign a string representing the current time to the variable CurrentTime$: 1. Type the following line (exactly as shown) on the next line in the Immediate window: CurrentTime$ = time$ 2. Press ENTER to execute the assignment statement you just typed. 3. Type the following line in the Immediate window, exactly as shown: print CurrentTime$ Figure 3.4 shows how the Immediate window should now look: File Edit View Search Run Debug Options Hel ┌──────────────────────────────── Untitled ───────────────────────────┤ │CLS │PRINT "This is my first QuickBASIC program" │PRINT 2 + 2 │ │ │ │ │ │ │ │ │ │ │ │ │ ├─────────────────────────────── Immediate ───────────────────────────── │cls : print "This line comes from the Immediate window" │CurrentTime$ = "" │CurrentTime$ = time$ │print CurrentTime$ │ <Shift+F1=Help> <F6=Window> <Enter=Execute Line> CN 00004: Figure 3.4 Immediate Window Showing Lines Just Entered 4. Press ENTER to display the value of CurrentTime$. The value of CurrentTime$ is displayed beneath the first line on the output screen. 5. Press a key to return to the environment. You can write up to 10 lines of statements in the Immediate window. If you type an eleventh line, the first line you typed is lost; if you type a twelfth, the second line you typed is lost, and so on. Section 10.5 illustrates other ways you can use the Immediate window. Monitoring Variables with the Watch Window When a program doesn't behave the way you expect, it is often because a variable is acquiring a value you did not anticipate. The Watch window lets you monitor the values of expressions while your program is running, so you can be sure their values are within the expected range. Try the following to see how the Watch window works: 1. Press F6 to move the cursor to the Immediate window if it is not already there. 2. Press ALT+D, then press A to choose the Debug menu's Add Watch command. QuickBASIC displays the Add Watch dialog box. 3. Type CurrentTime$, then press ENTER. The Watch window opens at the top of the screen. It contains the name from the View window's title bar, followed by CurrentTime$, the name of the variable you just entered (see Figure 3.5). The cursor returns to the Immediate window. Name from View window's title bar Variable name Watch window │ │ │ │ File Edit View Search│ Run Debug Options │ Hel └Untitled CurrentTime$: │ │ ┌─────────┴──────┬──────┴──┼───── Untitled ───────────────────────────┤ │CLS └─────────┘ │PRINT "This is my first QuickBASIC program" │PRINT 2 + 2 │ │ │ │ │ │ │ │ │ ├─────────────────────────────── Immediate ───────────────────────────── │cls : print "This line comes from the Immediate window" │CurrentTime$ = "" │CurrentTime$ = time$ │print CurrentTime$ │ <Shift+F1=Help> <F6=Window> <Enter=Execute Line> CN 00004: Figure 3.5 Placing Variables in the Watch Window 4. Press CTRL+HOME to place the cursor on the first line of the Immediate window, then press ENTER to execute each of the lines in the Immediate window. Look at the Watch window while you press ENTER on each line. As soon as the line CurrentTime$ = time$ is executed, you will notice that the value for CurrentTime$ appears in the Watch window. With the Watch window you can monitor variable values as they change in the running program without having to use PRINT statements to display the value on the output screen. The Help Window Most on-line help appears in the Help window. There are several ways to get help on BASIC keywords, such as PRINT and TIME$, and the QuickBASIC environment. You can use the Help menu or press F1 while an item on screen (or a menu or command) contains the cursor or is highlighted. ────────────────────────────────────────────────────────────────────────── NOTE If you get error messages when you try to access on-line help, check Section 10.8.4, "Help Files," for more information on how to set up help properly. ────────────────────────────────────────────────────────────────────────── Context-Sensitive Help With context-sensitive help, you can get information about BASIC keywords and program symbols. The following steps illustrate the use of context-sensitive help: 1. Press ESC to close the Help menu if it is open. 2. Use DIRECTION keys to move the cursor anywhere within the word PRINT. 3. Press F1. QuickBASIC displays a QuickSCREEN of the PRINT keyword (see Figure 3.6). File Edit View Search Run Debug Options Hel Untitled CurrentTime$: ┌───────────────────── HELP: PRINT Statement QuickSCREEN ─────────────┤ │ QuickSCREEN Details Example Contents Index │─────────────────────────────────────────────────────────────────────── │PRINT - a device I/O statement that outputs data on the screen │ │Syntax │ PRINT [expressionlist][{,|;}] │ │ = If all arguments are omitted, a blank line is printed. │ = If expressionlist is included, the values of the expressions are │ printed on the screen. │ = The expressions in the list may be numeric or string expressions. │ (String literals must be enclosed in quotation marks.) │ = The optional characters "'" and ";" are details. │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Untitled ────────────────────────────┤ ├─────────────────────────────── Immediate ───────────────────────────── │cls : print "This line comes from the Immediate window" │CurrentTime$ = "" │CurrentTime$ = time$ │print CurrentTime$ <Shift+F1=Help> <F6=Window> <Esc=Cancel> <Ctrl+F1=Next> <Alt+F1=Back> Figure 3.6 QuickSCREEN for PRINT Statement The QuickSCREEN briefly describes the statement's action, then gives the syntax and explains each part of it. At the bottom, the QuickSCREEN indicates other uses of the keyword. Hyperlinks At the top of the screen, several bracketed items, called "hyperlinks," indicate related topics you can investigate. Hyperlinks provide instant connections between related topics. At the bottom of the screen, the other uses of the keyword are also bracketed as hyperlinks. If you want more information on one of them, use the TAB key to move the cursor to the hyperlink, then press F1, as explained here. 1. Press F6 until the cursor appears into the Help window. 2. Press TAB to move the cursor to the Example hyperlink. 3. Press F1 to view the Example screen (see Figure 3.7). Hyperlinks to related topics │ │File Edit View Search Run Debug Options Hel ┌─┼─────────────── HELP: PRINT Statement Programming Examples ────────┤ │ │QuickSCREEN Details Example Contents Index │─┼──────────────────────┼─────────────┼──────────────┼────────────┼──── │ └──────────────────────┴─────────────┴──────────────┴────────────┘ │PRINT Statement Programming Examples │ │Example 1 │ │In the following example, the commas in the PRINT statement │print each value at the beginning of the next print zone: │ │X=5 │PRINT X+5, X-5, X*(-5), X^5 │END │ │Sample Output │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Untitled ────────────────────────────┤ ├─────────────────────────────── Immediate ───────────────────────────── │cls : print "This line comes from the Immediate window" │CurrentTime$ = "" │CurrentTime$ = time$ │print CurrentTime$ <Shift+F1=Help> <F6=Window> <Esc=Cancel> <Ctrl+F1=Next> <Alt+F1=Back> Figure 3.7 Example Screen for PRINT Statement You can scroll within the Help window to examine all the PRINT examples. 4. Press ALT+F1 once or twice to return to the screen you linked from. 5. Repeat steps 1 and 2 to view the information available through the other bracketed hyperlinks. You can use several successive hyperlinks without returning to the previous screen, QuickBASIC keeps track of the last 20 hyperlinks. You can use ALT+F1 to go back through the sequence of hyperlinks. When you reach the screen from which you started, QuickBASIC beeps if you press ALT+F1. You can press ESC any time to clear the Help window completely, even if you are several levels down in hyperlink screens. For a reminder on which keys or key combinations to use for moving in or among Help screens, choose Contents from the Help menu, then choose the "Help keys" hyperlink. Also, SHIFT+F1 gives a general explanation of help. Even some items that are not bracketed are hyperlinks. Press F1 any time you have a question about anything on the QuickBASIC screen. If QuickBASIC has more information on it, the information appears in the Help window; if no other information is available, QuickBASIC beeps. ────────────────────────────────────────────────────────────────────────── NOTE You cannot edit text in the Help window, but you can edit text in the View window or Immediate window while the Help window is open. In Chapter 8, "Using Example Code from On-Line Help," you'll learn to copy text from the Help window and paste it into your program. ────────────────────────────────────────────────────────────────────────── Exiting from QuickBASIC and Saving Programs The following steps explain how to exit QuickBASIC and return to the DOS command line: 1. Press ALT+F, then press X to exit from QuickBASIC. A dialog box appears asking if you want to save the unsaved material in the View window. 2. Press ENTER to tell QuickBASIC that you want to save the program in the View window. QuickBASIC displays the Save As dialog box (see Figure 3.8): ┌─Type your program name here │ ┌────────────────┼───── Save As ──────────────────┐ │ │ │ │ ┌──┴───────────────────────────────┐│ │ File Name: │ ││ │ └──────────────────────────────────┘│ │ C:\QB4.5\DEMO │ │ │ │ Dirs/Drives │ │ ┌──────────────┐ ┌─────── Format ────────┐ │ │ │.. │ (∙) QuickBASIC - │ │ │ │SOURCE ░ │ Fast Load and │ │ │ │[-A-] ░ │ Save │ │ │ │[-B-] ░ │ │ │ │ │[-C-] ░ │ ( ) Text - │ │ │ │[-U-] ░ │ Readable by │ │ │ │[-Z-] │ Other Programs │ │ │ └──────────────┘ └───────────────────────┘ │ ├─────────────────────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └─────────────────────────────────────────────────┘ Figure 3.8 Save As Dialog Box 3. Type program1 in the text box. 4. Press ENTER to save the lines in the View window on disk with the file name PROGRAM1.BAS. For More Information For more information on the topics covered in this chapter, see the following: Where to Look What You'll Find ────────────────────────────────────────────────────────────────────────── Chapter 9, "Debugging While You Debugging techniques and using the Program," and Chapter 17, Watch window "Debugging Concepts and Techniques" Section 10.5, "Using the Immediate Ways to use the Immediate window Window" Chapter 11, "The File Menu" Opening, clearing, and saving files in QuickBASIC ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 4 Interlude: BASIC for Beginners This chapter introduces the general principles of programming in BASIC. The focus is on the fundamentals, so you can start programming quickly. If you have never programmed before, you should read this chapter carefully. When you finish this chapter, you will be able to write simple BASIC programs. You may want to read some intermediate-level books on BASIC before tackling advanced programming techniques in the following chapters. If you already have programming experience with BASIC, you may want to skim this chapter to get a general idea of the differences between Microsoft BASIC and the BASIC dialect you know. Many brief programming examples are given to show how each element of BASIC works. The quickest way to learn BASIC is to enter and run these examples as you read. You can enter multi-line examples in the View window. Or you can enter single-line examples in QuickBASIC's Immediate window, then press ENTER to see the resulting output. Study each example to understand why it works the way it does. Be sure you grasp the material in one section before going on to the next. When you have completed this chapter, you will understand how to ■ Display words and numbers on the screen ■ Define and use variables ■ Perform calculations and use BASIC's math functions ■ Use arrays of variables ■ Execute sections of your program selectively ■ Repeat a group of instructions a specific number of times or until a condition is met What is a Program? A "program" is a sequence of instructions to the computer, in a language both you and the computer understand. Each instruction is called a "statement" and usually takes up one line in the program. The goal of any program is to perform some useful job, such as word processing, bookkeeping, or playing a game. Programming is the process of deciding what you want the program to do. Then you select and arrange language statements to accomplish the individual tasks needed to reach the overall goal. This process is part science, part art. The science comes from books; the art is learned by writing your own programs and analyzing programs written by others. Many BASIC statements have additional features that are not described in this chapter. If you want more information about a particular statement or language feature, please refer to Chapter 8, "Statement and Function Summary," in Programming in BASIC or consult QuickBASIC's on-line help. Comments Comments are an important part of programming. They explain the program to others, and remind you why you wrote it the way you did. Comments begin with an apostrophe, and can extend to the end of the line, as follows: ' This is a comment. CLS ' The CLS statement clears the screen. The apostrophe tells QuickBASIC that everything between the apostrophe and the end of the line is a comment. Displaying Words and Numbers on the Screen You are probably familiar with application software such as Lotus(R) 1-2-3(R) or Microsoft Word. These and most other programs communicate with the user by displaying words, numbers, and data on the screen. The PRINT statement is BASIC's command for writing on the screen. Two of the things PRINT can display are strings and numbers. A "string" is any group of characters (letters, numbers, punctuation marks) enclosed in quotes. The following example program shows how the PRINT statement displays a string: 1. Start QuickBASIC (if it is not already started) by typing qb and pressing ENTER. 2. Type the following line in the Immediate window, then press ENTER: PRINT "Hello, world" The output should appear as follows: Hello, world The quotes that surround a string are not part of the string, so they do not appear in the display. 3. Type CLS in the Immediate window and press ENTER to clear the output screen. ────────────────────────────────────────────────────────────────────────── NOTE BASIC is not case sensitive; you don't have to enter the examples with the cases as shown. QuickBASIC automatically capitalizes words that are part of the BASIC language but leaves everything else as you enter it. The examples in this chapter are shown the way QuickBASIC formats them, and each program's output is shown exactly as it appears on the screen. ────────────────────────────────────────────────────────────────────────── The PRINT statement can also display numbers as shown in the following example program: 1. Type the following line in the Immediate window, then press ENTER: PRINT 63 The output should appear as follows: 63 2. Type CLS in the Immediate window and press ENTER to clear the output screen. Variables Programs take data from the outside world (input), then process it to produce useful information (output). The input and output data are stored in the computer's memory. Variable names are used to keep track of where the data are stored. Storing Data in Memory Computer memory is divided into storage locations, each of which has a unique "address." The address is a number that gives the memory location, the same way your house address shows where you live on a street. Every piece of data has its own storage location and matching address (see Figure 4.1). ┌─────────────────────────────────────────────────────────┐ │ │ │ ┌──────┬──────┬──────┬──────┬──────┬──────┬──────┐ │ │ │ 1230 │ 1231 │ 1232 │ 1233 │ 1234 │ 1235 │ 1236 │ │ │ └──────┴──────┴──────┴──────┴──────┴──────┴──────┘ │ │ │ └─────────────────────────────────────────────────────────┘ Figure 4.1 Addresses in Memory Fortunately, you don't have to keep track of the address for every data item. BASIC uses a "variable name" to associate a word of your choice with a memory location in the computer. BASIC does the associating automatically. Every time you use a variable name that BASIC hasn't seen before, BASIC finds an unused memory location and associates the new variable name with that address. You can then use the variable name without having to know its address. The following example program demonstrates this. Note that Hello, world is not enclosed in quotes in this example. 1. Type the following line in the Immediate window, then press ENTER: PRINT Hello, world The output should appear as follows: 0 0 2. Type CLS in the Immediate window and press ENTER to clear the output screen. When BASIC encounters Hello and world, it has to decide what these words are. They aren't keywords (that is, they aren't part of the BASIC language), as PRINT is. They aren't strings, because they aren't enclosed in quotes. They are definitely not numbers. Therefore, Hello and world must be variables. Once this decision is made, BASIC sets aside storage space for two new variables named Hello and world. New variables are always given an initial value of zero, so the PRINT statement displays two zeros. A variable name can contain digits, but the name cannot begin with a digit. Any word starting with a digit is interpreted as a number. Names allowed in BASIC include: gerbils birthdate name3 ep45lp33 These are illegal names: 5remove 4.3less Variable Types Data do not come in just one form. Programming languages, therefore, need different types of variables to hold different types of data. BASIC has three categories of variables: integer, floating point, and string. Integer Variables An integer number is a whole number, without a fractional part. For example, 0, -45, and 1278 are integers. Integer numbers are stored in integer variables. BASIC has two types of integer variables: integer and long integer. A variable name ending in % is an integer variable. Integer variables can have any whole-number value between -32,768 and 32,767. A variable name ending in & is a long-integer variable and can have any whole-number value between -2,147,483,648 and 2,147,483,647. Floating-Point Variables A floating-point number can have a fractional part (though it doesn't have to). For example, 0.123, 78.26, 7.0, and 1922.001234 are all floating-point numbers. Floating-point numbers are stored in floating-point variables. BASIC has two types of floating-point variables: single precision and double precision. A variable name ending in a letter, a digit, or ! is a single-precision floating-point variable. Single-precision floating-point numbers can have values ranging from about -3.4 x 10'38 to 3.4 x 10'38 (that's 34 with 37 zeros following). A single-precision floating-point variable is accurate to only about 7 decimal places. A variable name ending in # is a double-precision floating-point variable and can have values from about -1.7 x 10'308 to 1.7 x 10'308 (that's 17 with 307 zeros following!). A double-precision floating-point variable can hold much larger numbers than a single-precision variable, and it is also more accurate── to about 15 decimal places. Single-precision floating-point numbers are the kind most often used in calculations, since "real-world" applications usually need numbers with fractional parts. (Prices are a good example.) Since single-precision floating-point variables are so commonly used, they are the "default" data type; that is, if a variable name does not end with a "type" character (%, &, #, !, or $), it is assumed to be a single-precision floating-point variable. Note, however, that calculations with integer variables take much less computer time than those performed with floating-point variables. Integer variables should be used when speed is required. The numerical variables in the remaining examples in this chapter are marked with the appropriate type suffix, either ! or %. Although most of these are single-precision floating-point variables, which need no type suffix, they are given the ! suffix for clarity. String Variables A string variable holds a sequence (a string) of characters. A variable name ending in $ is a string variable. Just as a numeric variable is given an initial value of 0, a newly defined string variable is assigned an initial length of zero. It contains no data at all, not even blank spaces. If blank$ has not previously been given a value, the statement PRINT blank$ displays an empty line. Assigning Values to Variables A variable gets its value through an "assignment" statement. An assignment statement has three components: the variable that receives a new value; an equal sign (=); and the number, string, or calculation whose value the variable takes on. These are all valid assignment statements: age% = 41 myname$ = "Willie" result! = result3! + leftval! + rightval! In the next example program, two strings are combined with the plus sign (+) to make a longer string. The result is assigned to a third string. 1. Choose the File menu's New Program command to clear the View window (press ALT+F, then press N). 2. Type the following example in the View window: string1$ = "Hello," string2$ = " there!" bigstring$ = string1$ + string2$ PRINT bigstring$ 3. Choose the Run menu's Start command (press ALT+R, then press S). The output should look like the following: Hello, there! 4. Type CLS in the Immediate window and press ENTER to clear the output screen. Although assignment is shown by the equal sign, it is not the same thing as algebraic equality. To BASIC, the assignment statement means: "Perform all the calculations and data manipulations on the right side of the equal sign. Then give the variable on the left side the result." The same variable name can appear on both sides of the assignment statement. This occurs most often when you want to change the variable's value. Try the following example program: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: counter% = 6 PRINT counter% counter% = counter% - 1 PRINT counter% 3. Choose the Run menu's Start command. The output should look like the following: 6 5 4. Type CLS in the Immediate window and press ENTER to clear the output screen. You cannot assign numeric values to string variables (or vice versa). Therefore, the following statements are illegal. Either one halts execution and causes the error message Type mismatch when the program runs. strg$ = 3.14159 number! = "hi, there" Calculations In BASIC, the mathematical operations of addition, subtraction, multiplication, and division are represented by +, -, * (the asterisk), and / (the slash), respectively. Exponentiation (raising a number to a power) is shown by ' (the caret). You can type each of the following on a line in the Immediate window, then press ENTER to see the results of the operations: Operation Result ────────────────────────────────────────────────────────────────────────── PRINT 2 + 3 5 PRINT 2 - 3 -1 PRINT 2 * 3 6 PRINT 2 / 3 .6666667 PRINT 2 ' 3 8 ────────────────────────────────────────────────────────────────────────── Integer Division and the Remainder Operator BASIC has two math operations you may not have seen before, integer division and the remainder operator. Integer division retains the integer (whole-number) part of the division and discards the fractional part. Integer division is represented by \ (the backslash). You can type each of the following on a line in the Immediate window, then press ENTER to see the results of the operations: Operation Result ────────────────────────────────────────────────────────────────────────── PRINT 7 \ 3 2 PRINT 9.6 \ 2.4 5 ────────────────────────────────────────────────────────────────────────── Both integer division and the remainder operator round off the numbers to be operated on before the calculation is performed. The number 9.6 becomes 10 and 2.4 becomes 2. Therefore, the result of the second example above is 5, not 4. The remainder operator is the complement of integer division. The whole-number part of the division is discarded, and the remainder is returned. Remainder division is performed by the BASIC keyword MOD. You can type each of the following on a line in the Immediate window, then press ENTER to see the results of the operations: Operation Result ────────────────────────────────────────────────────────────────────────── PRINT 7 MOD 3 1 PRINT 11 MOD 4 3 ────────────────────────────────────────────────────────────────────────── Precedence of Operations BASIC evaluates mathematical expressions from left to right, following the rules of algebraic precedence: exponentiation is performed first, then multiplication and division, then addition and subtraction. The following example program illustrates algebraic precedence: 1. Type the following line in the Immediate window, then press ENTER: PRINT 2 * 3 + 2 ' 3 - 2 / 3 The output should appear as follows: 13.33333 2. Type CLS in the Immediate window and press ENTER to clear the output screen. Parentheses can confirm or override the normal precedence. Try this example: 1. Type the following line in the Immediate window, then press ENTER: PRINT (2 * 3) + (2 ' 3) - (2 / 3) The output should appear as follows: 13.33333 2. Type CLS in the Immediate window and press ENTER to clear the output screen. The result is the same as in the last example because the precedence of operations dictated by the parentheses is no different from the usual order. However, the next example program produces a different result: 1. Type the following line in the Immediate window, then press ENTER: PRINT 2 * (3 + 2) ' (3 - 2 / 3) The output should appear as follows: 85.49879 2. Type CLS in the Immediate window and press ENTER to clear the output screen. The result here is different because the calculations within parentheses are performed first. Within parentheses, the usual precedence still applies, of course. The expression (3 - 2 / 3) evaluates as (3 - .6666667), not (1 / 3). You might want to use parentheses to control the order of calculations, rather than depending on precedence. Parentheses prevent errors and make your programs easier to understand. Math Functions Along with the addition, subtraction, multiplication, and division operators just presented, BASIC provides a number of common math functions, described briefly below. To use them, follow the function name with the variable or expression you want the function performed on (in parentheses). The expression may be any valid combination of variables, numbers, and math functions. (Expressions are explained further in the following section.) Function Description ────────────────────────────────────────────────────────────────────────── ABS Returns the absolute value of the expression ATN Returns the angle (in radians) whose tangent equals the expression COS Returns the cosine of an angle (in radians) EXP Returns e to the power of the expression LOG Returns the logarithm of the expression SGN Returns -1 if the expression is less than 0; returns 0 if it is 0; returns +1 if it is greater than 0 SIN Returns the sine of an angle (in radians) SQR Returns the square root of the expression TAN Returns the tangent of an angle (in radians) ────────────────────────────────────────────────────────────────────────── The following example program shows the use of the square-root function: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: adjacent! = 3.0 opposite! = 4.0 hypotenuse! = SQR((adjacent! ' 2) + (opposite! ' 2)) PRINT "the hypotenuse is:"; hypotenuse! 3. Choose the Run menu's Start command. The output should look like the following: the hypotenuse is: 5 4. Type CLS in the Immediate window and press ENTER to clear the output screen. Expressions An "expression" is what most people would call a formula. An expression is any combination of numbers, strings, variables, functions, and operators that can be evaluated. For example, 2 + 2 is a simple expression. It evaluates to four. Enter the following statements in the View window to assign a variety of simple expressions to variables, as follows: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: square% = 3 ' 2 root! = SQR(3 ' 2) greeting$ = "Hello," + " world! " strange! = 9 + "cats" The last statement you typed was illegal. 3. Choose the Run menu's Start command. QuickBASIC displays the error message Type mismatch. You cannot add a number (or numerical variable) to a string (or string variable). 4. Type CLS in the Immediate window and press ENTER to clear the output screen. Expressions may be as complex as you like, with the results of one expression passed to a function, the value returned by a function combined with other expressions, and so on. Almost any place you can use a number or a string, you can use any expression (no matter how complex) that evaluates to a number or a string. This means expressions can be used in BASIC's math functions, PRINT statements, and assignment statements. Displaying Variables and Expressions The PRINT statement was first shown in this chapter as a way to display numbers and strings. The PRINT statement can also display the values of variables and expressions. For example, try this: 1. Type the following lines in the Immediate window, then press ENTER: PRINT (2 + 8) / 4 + 1 The output should appear as follows: 3.5 2. Type CLS in the Immediate window and press ENTER to clear the output screen. The PRINT statement is quite flexible; it can display any combination of strings, numbers, variables, and expressions. The items to be displayed are separated by semicolons (;) or commas (,). When a semicolon separates two items, the second item is displayed immediately after the first, as shown in the example program below: 1. Type the following line in the Immediate window, then press ENTER: PRINT "Sum of 5.29 and"; 2.79; "is"; 5.29 + 2.79 The output should appear as follows: Sum of 5.29 and 2.79 is 8.08 2. Type CLS in the Immediate window and press ENTER to clear the output screen. Here's another example program to try: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: number = 36 PRINT "The sum of"; number; "and 4 is"; number + 4 PRINT "The square of"; number; "is"; number * number 3. Choose the Run menu's Start command. The output should look like the following: The sum of 36 and 4 is 40 The square of 36 is 1296 4. Type CLS in the Immediate window and press ENTER to clear the output screen. If two items in a PRINT statement are separated by a comma, the second item is positioned at the next preset tab location. (The tab stops are 14 columns apart.) Note the difference between the output of the following PRINT statement and that of the similar one with semicolons, above: 1. Enter the following lines in the Immediate window, then press ENTER: PRINT "Sum of 5.29 and", 2.79, "is", 5.29 + 2.79 The output should appear as follows: Sum of 5.29 and 2.79 is 8.08 2. Type CLS in the Immediate window and press ENTER to clear the output screen. Commas and semicolons can be used in the same PRINT statement to position the items any way you like. Each PRINT statement normally places its output on a new line, as the following example program shows: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: PRINT "How old are you?" PRINT 41 The output should appear as follows: How old are you? 41 3. Choose the Run menu's Start command. 4. Type CLS in the Immediate window and press ENTER to clear the output screen. If you want to combine the output of several PRINT statements on the same line, place a semicolon (;) at the end of each PRINT statement. Change the last example program as follows: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: PRINT "How old are you?"; PRINT 41 3. Choose the Run menu's Start command. The output should look like the following: How old are you? 41 4. Type CLS in the Immediate window and press ENTER to clear the output screen. Entering Data with the INPUT Statement The INPUT statement displays a prompt string, then waits for the user to enter some value. The value entered in response to the prompt is assigned to the variable specified in the INPUT statement. INPUT "enter your age: ", age% PRINT age% If you typed 39 in response to the enter your age: prompt, the value 39 would be assigned to the variable age%, and that value would be printed by the following PRINT age% statement. INPUT also accepts strings: INPUT "What is your name? ", yourname$ PRINT yourname$ A string variable will accept whatever you type, since all entries──even numbers──are actually strings. (When you type 42, you are not typing the number 42, but rather the characters 4 and 2. If the input variable is numerical, BASIC converts this string into a number. If the input variable is a string, the character sequence 42 is simply assigned to the string.) A numeric variable, however, can only be assigned a number. If you type dog when you should have entered a number, BASIC responds with the message Redo from start and a new prompt line. Arrays of Variables If you wanted to keep track of the high temperature for each day in July, you could use 31 floating-point variables, named july1, july2, july3, and so on through july31. However, a group of related but individually named variables is clumsy to work with; each variable has to be handled separately. For example, if you wanted to prompt the user for each temperature in July, you would have to write 31 individual prompt statements. INPUT "What is the temp value for July 1? ", july1 . . . INPUT "What is the temp value for July 31? ", july31 An analogous problem occurs when you're trying to write a program that retrieves the stored data. You wouldn't want to write a program that displayed all 31 variable names to be able to retrieve the value for any specific one (say, the high temperature for July 4──the value for july4). It would be much more convenient if you could just give the computer the date (the number 4) and the computer would select the right variable and value. The solution is to give the entire set of values the same name (july in our example) and distinguish the individual values by a numerical index called a "subscript." A group of identically named variables distinguished by their subscript values is called an "array." (See Figure 4.2 for an example.) Arrays can be especially powerful when used in conjunction with loops (see the section titled "Repeating Program Operations"). ┌─────────────────────────────────────────────────────────────────┐ │ │ │ ┌───────────┬───────────┬───────────┬───────────┬───────────┐ │ │ │ Price (0) │ Price (1) │ Price (2) │ Price (3) │ Price (4) │ │ │ └───────────┴───────────┴───────────┴───────────┴───────────┘ │ │ │ └─────────────────────────────────────────────────────────────────┘ Figure 4.2 Array Created by the BASIC Statemenet DIM Price (4) Declaring Arrays An array variable must first be "declared" with a DIM statement, which establishes the size of the array. A DIM statement must appear before the array variable can be used. The value given in the DIM statement specifies the maximum value for the variable's subscript. For example, the following statement declares an array of 32 floating-point variables named july, whose subscripts run from 0 to 31: DIM july(31) DIM also works with string variables: DIM stringvar$(250) Specifying Array Elements You can specify the nth member (or "element") of an array simply by putting the number n (or a variable or expression with the value n) in parentheses following the variable name. In this way the program can connect a specific variable with a number entered by the user. For example, the fourth element of the july array could be specified by either july(4) or──if d% equals four──july(d%) or even july(SQR(16)). The following code fragment prompts the user for the date, then prints the high temperature for that day in July (assuming that all the temperatures have been assigned to the array july). DIM july(31) INPUT "enter July date: ", date% PRINT "high temperature for July"; date%; "was"; july(date%) Logical Relations Used in Decision-Making BASIC can decide whether two numbers or strings are the same or different. On the basis of such a decision, an appropriate group of program statements can be executed or repeated. For example, suppose the standard income-tax deduction is $2500. If your itemized deductions are less than $2500, you would take the standard deduction. If your itemized deductions are greater than $2500, you would itemize. An income-tax program can make this decision and execute either the part of the program that performs itemized deductions or the part that takes the standard deduction. The user doesn't have to tell the program what to do. The following sections explain how BASIC makes logical decisions that can be used in your programs. Relational Operators Numbers and strings are compared using "relational operators." There are six possible relationships, shown by the following operators: Relational Operator Meaning ────────────────────────────────────────────────────────────────────────── = Equal to <> Not equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── NOTE BASIC uses the equal sign (=) both to assign a value to a variable and also to indicate logical equality. BASIC knows which usage is intended from the context. ────────────────────────────────────────────────────────────────────────── The following list shows how these relationships are evaluated: Relational Operation Evaluation ────────────────────────────────────────────────────────────────────────── 7 = 35 False 7 <> 6 True 6 > 1 True 4 < 3 False 7 <= 7 True 8 >= 7 True apples = oranges Depends on values of variables ────────────────────────────────────────────────────────────────────────── As for the last statement──apples aren't oranges. But if apples and oranges were variable names, then the truth or falsity of the statement would depend on the values of these variables. The following relational operations compare strings. Are they true or false? "Tarzan" <> "Jane" "Y" = "Y" "Y" = "y" "miss" > "misty" Tarzan and Jane are different strings, so the first assertion is true. Y and Y are the same character, so the second assertion is true. Y and y are not the same character, so the third assertion is false. The last statement may be confusing at first; how can one string be "larger" or "smaller" than another? It can be, and the decision is made this way. The strings are first compared, position by position, until BASIC finds characters that don't match. In this example, the fourth characters are the first nonmatching characters. The decision of "larger" or "smaller" is then based on these differing characters, in the following way. Within the computer, characters are represented by numbers. Letters coming later in the alphabet have numeric values larger than those appearing earlier. Since t follows s in the alphabet, t is a "larger" letter, and the statement is therefore false; misty is "larger" than miss. This ability to determine the relative value of strings makes it easy to write a program that can alphabetize a list of words or names. In most of these examples, numbers were compared with numbers and strings with strings. But any combination of numbers and numerical variables can be compared; the same is true for strings and string variables. The only things you cannot compare are numerical values with string values because the comparison is logically meaningless. Boolean Expressions Logical assertions are called "Boolean expressions" (for George Boole, who formulated some of the rules of mathematical logic). Boolean operations are concerned with only one thing: is a Boolean expression true or false? Unlike mathematical expressions, which evaluate to numbers, Boolean expressions evaluate to one of two values: "true" or "false." Computers use numbers to represent "true" and "false." To see how BASIC codes "true" and "false," enter and run these two lines, as follows: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: PRINT 5 > 6 PRINT 6 > 5 3. Choose the Run menu's Start command. The output should look like the following: 0 -1 The display shows 0 on the first line, -1 on the second. The number 5 is not greater than 6, so BASIC prints its value for "false": 0. The number 6 is greater than 5, so BASIC prints its value for "true": -1. 4. Type CLS in the Immediate window and press ENTER to clear the output screen. Compound Expressions In BASIC, a compound Boolean expression is created by connecting two Boolean expressions with a "logical operator." The two most commonly used logical operators are AND and OR. The AND operator requires both expressions to be true if the compound expression is to be true. When the OR operator is used, only one of the expressions has to be true for the compound expression to be true. The following examples are compound expressions that combine two simple expressions by using AND or OR: Expression Evaluation ────────────────────────────────────────────────────────────────────────── 10 > 5 AND 100 < 200 True 3 < 6 AND 7 > 10 False 8 < 7 OR 90 > 80 True 2 < 1 OR 3 > 60 False "Y" > "N" AND "yes" <> "no" True "Y" < "N" OR 4 <> 4 False ────────────────────────────────────────────────────────────────────────── The NOT operator reverses the truth or falsity of an expression: Expression Evaluation ────────────────────────────────────────────────────────────────────────── NOT (5 > 10) True NOT (8 < 7 OR 90 > 80) False NOT (3 < 6 AND 7 > 10) True NOT (0) True ────────────────────────────────────────────────────────────────────────── The logic of the last example may not be immediately obvious. In BASIC, false is zero. Therefore, NOT (0) means "not false," or true. Combinations of AND, OR, and NOT can be used to build up very complex expressions. There is no practical limit to their complexity, except the obvious one of writing an expression that is difficult to read. When Boolean expressions are evaluated, the precedence of evaluation is taken in the same order as arithmetic expressions, with AND equivalent to multiplication and OR equivalent to addition. Evaluation goes from left to right, with all the simple expressions evaluated first. All the AND-connected expressions are evaluated next, followed by the OR-connected expressions. As with arithmetic expressions, parentheses can be used to control the order of evaluation, rather than relying on the rules of precedence. See Chapter 1, "Control-Flow Structures," in Programming in BASIC, for more explanation of why BASIC considers -1 equivalent to true. The next sections show how Boolean expressions are used in programs. Using Logical Statements to Control Program Flow You are always deciding what to do next by evaluating your priorities and desires, asking yourself which is most important at the moment. Similarly, BASIC has a mechanism that allows your program to select which set of operations (that is, which part of the program) will be executed next. This mechanism is the IF...THEN...ELSE statement. If a Boolean expression is true, the statements following THEN are executed. If the expression is false, the statements following ELSE are executed. A Boolean expression must be either true or false, so one or the other group of statements has to execute. Both cannot execute. The process of selecting among two or more possible actions (or sections of program code) is called "branching." The analogy is with the way a tree branch subdivides into more and more branches. This is the syntax of the IF...THEN...ELSE statement: IF booleanexpression THEN statements to do something ELSE statements to do something else END IF Try the following simple example to use the IF...THEN...ELSE statement to decide whether a number entered is greater than, less than, or equal to 100: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: INPUT "enter a number: ", n IF n > 100 THEN PRINT n; "is greater than 100" ELSE PRINT n; "is less than or equal to 100" END IF 3. Choose the Run menu's Start command. The logical opposite of "greater than" is "less than or equal to" (not "less than"). Run this example with several values for n, including a value of 100 to verify that the is less than or equal to 100 statement is displayed. 4. Type CLS in the Immediate window and press ENTER to clear the output screen. See Chapter 1, "Control-Flow Structures," in Programming in BASIC for a more detailed explanation of the IF...THEN...ELSE statement and other decision structures available in QuickBASIC. Repeating Program Operations BASIC offers several ways to execute a group of program statements repeatedly. You can repeat them a fixed number of times or until a particular logical condition is met. If you want to execute a block of statements 100 times, you need only type them in once. BASIC's control structures then control the repetitions. The ability to repeat program statements has many uses. For example, to raise a number N to the power P, N must be multiplied by itself P times. To enter data for a ten-element array, you must prompt the user ten times. The FOR...NEXT Loop One way to repeat a section of the program is the FOR...NEXT loop. The block of program statements between the FOR and NEXT keywords is executed repeatedly a specified number of times. Try the following: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: FOR count% = 1 TO 5 PRINT "this line is printed 5 times; this is time"; count% NEXT count% 3. Choose the Run menu's Start command. The output should look like the following: this line is printed 5 times; this is time 1 this line is printed 5 times; this is time 2 this line is printed 5 times; this is time 3 this line is printed 5 times; this is time 4 this line is printed 5 times; this is time 5 4. Type CLS in the Immediate window, then press ENTER to clear the output screen. In the example above, the variable count% is called the "loop variable" or "loop counter." The two numbers after the equal sign (separated by the keyword TO) are the start and end values for the loop counter. In this example, 1 is the start value, and 5 is the end value. Before the statements in the FOR...NEXT loop are executed for the first time, the loop counter is given the start value (in this case, 1). After each execution of the statements in the loop, BASIC automatically increments count% by one. This cycle continues until count% is larger than the end value (in this case, 5). The statements between the FOR and NEXT keywords in this example are therefore executed five times. To repeat a FOR...NEXT loop n times, the start and end values would normally be 1 and n. This is not a necessity, though. They can have any two values that differ by n - 1. For example, using -2 and 2 would also cause five repetitions. The counter can be the subscript variable for an array. (Accessing each element in an array is a common use for a FOR...NEXT loop.) The next example prompts the user for the high temperature on each day in July: DIM july!(31) FOR date% = 1 TO 31 PRINT "enter the high temp for July"; date%; INPUT " ", july!(date%) NEXT date% Neither the start nor the end value has to be a constant; either or both can be a variable. The following example requests start and end values, then prints out the square root of every value in that range: INPUT "starting value? ", startval% INPUT "ending value? ", endval% FOR count% = startval% TO endval% PRINT "the square root of"; count%; "is"; SQR(count%) NEXT count% The increment defaults to a value of one if it isn't specified. The STEP statement sets a different increment value, as shown in the following procedure: 1. Choose the File menu's New Program command to clear the View window. 2. Type the following example in the View window: FOR count% = 5 TO 1 STEP -1 PRINT "this line is printed 5 times; this is time"; count% NEXT count% 3. Choose the Run menu's Start command. The output should look like the following: this line is printed 5 times; this is time 5 this line is printed 5 times; this is time 4 this line is printed 5 times; this is time 3 this line is printed 5 times; this is time 2 this line is printed 5 times; this is time 1 4. Type CLS in the Immediate window, then press ENTER to clear the output screen. The step value must be consistent with the start and end values. If the end value is larger than the start value, the step must be positive. If the end value is smaller than the start value, the step must be negative. If the step has the wrong sign, the FOR...NEXT loop doesn't execute even once; it is skipped over. The DO...LOOP You have just seen one way to repeat a section of the program, the FOR...NEXT loop. The FOR...NEXT loop, however, has a serious limitation. Although you can specify the starting and ending points, the loop itself is fixed; it repeats a specific number of times, no more and no less. This caused no problem in the example where you were prompted for the 31 high temperatures in July, because July always has 31 days. However, there are times you can't know how often to repeat a calculation or an operation. Suppose you were searching through text, one line at a time, for a specific word. You don't know which line the word is on (if you did, you wouldn't have to search), so you can't specify the number of times to go through a FOR...NEXT loop. You need a flexible (rather than fixed) way to repeat groups of program statements. The DO...LOOP is the more flexible mechanism for repetition needed here. Program statements between the DO and LOOP keywords are repeated an indefinite number of times. Try the following example: 1. Choose the File menu's New Program command to clear the View window: 2. Type the following example in the View window. DO PRINT "Going around in circles..." LOOP 3. Choose the Run menu's Start command. Going around in circles... is printed over and over, without end. (To stop the program, press CTRL+BREAK.) 4. Type CLS in the Immediate window and press ENTER to clear the output screen. The simple DO...LOOP shown above is endless. BASIC has a way to terminate the loop at the right time. All you have to do is specify the logical condition you want to cause termination. One way to do this is to use a WHILE condition, which tells the computer to continue executing the loop WHILE some condition is true. Another is to use an UNTIL condition, meaning continue executing the loop UNTIL some condition becomes true. In a DO WHILE loop, the condition starts off true, and the loop executes as long as the condition remains true. In a DO UNTIL loop, the condition starts off false, and the loop executes until the condition becomes true. The user-defined condition is a Boolean expression. This expression usually compares a variable with a constant. When the expression satisfies the logical condition set by the programmer (such as the variable equalling the constant), the loop terminates. (Any comparison is possible, but comparing the loop variable with a number or string is the most common.) The DO WHILE Loop A DO WHILE loop looks like this: DO WHILE booleanexpression statements to be repeated LOOP Here is a simple DO WHILE loop that demonstrates how such a loop operates. The loop termination condition is for big! to equal little!. big! = 256.0 little! = 1.0 DO WHILE big! <> little! PRINT "big ="; big!; " little ="; little! big! = big! / 2.0 little! = little! * 2.0 LOOP Two variables, big! and little!, are initialized outside the loop. Within the loop, their values are first printed, then big! is divided by 2 and little! is multiplied by 2. The process repeats until both are equal to 16 and the loop terminates. The initial values of big! and little! were chosen to guarantee that they would eventually be equal. If they are not so chosen, the loop repeats indefinitely. (In practice, the program eventually stops regardless of the values chosen. The variable little! is repeatedly doubled, ultimately becoming so large that its value cannot be represented by a BASIC floating-point variable. The program then halts, displaying an Overflow error message.) Please note that for a DO WHILE loop to execute even once, the Boolean expression must be true. If big! and little! started with the same value, the expression big! <> little! would be false, and the loop would not execute at all; it would be skipped over. Always be sure the variables in the Boolean expression have the values you really want before entering the loop. The DO UNTIL Loop A DO UNTIL loop is identical in form to a DO WHILE loop, except it uses the keyword UNTIL: DO UNTIL booleanexpression statements to be repeated LOOP The loop shown in the last example could also have been written using UNTIL, as shown here: big! = 256.0 little! = 1.0 DO UNTIL big! = little! PRINT "big ="; big!; " little ="; little! big! = big! / 2.0 little! = little! * 2.0 LOOP A DO UNTIL loop continues until the Boolean expression becomes true, so a different terminating condition is needed. In this case, it is the opposite of the condition in the DO WHILE example above: big! = little!. The following is a more practical example of a DO...LOOP. The user is repeatedly prompted for a Yes / No response (indicated by Y or N) until it is supplied: DO UNTIL instring$ = "Y" OR instring$ = "N" INPUT "enter Yes or No (Y/N): ", instring$ LOOP PRINT "You typed"; instring$ Note that y and n are not accepted, since instring$ is compared only with uppercase characters. ────────────────────────────────────────────────────────────────────────── NOTE In the loop examples given, both the WHILE and UNTIL statements are located after DO. It is also possible to place them following the LOOP keyword. When that is done, the statements in the loop are executed first, then the condition is tested. This assures that the loop will always be executed at least once. See Chapter 1, "Control-Flow Structures," in Programming in BASIC, for an explanation of how this works. ────────────────────────────────────────────────────────────────────────── Writing a Simple BASIC Program If you've worked through the examples, you should now know the fundamentals of programming in BASIC. To demonstrate your understanding, try writing the simple program described below. The program computes the average of several numbers. It could be written in the following sequence: 1. Prompt the user for the quantity of numbers to be averaged. 2. If the quantity is zero or negative, print a warning message and do nothing else. 3. If the quantity is positive, pick a variable name for the running total and set it equal to zero. 4. Prompt for the numbers, one at a time. Tell the user each time which value is being entered (number 1, number 2, and so on). 5. When all the numbers have been entered, compute and print the average value. This program uses only BASIC language elements that have been explained in this chapter, and no programming "tricks" are needed. A solution is given below, but please try to create your own program before peeking. This is an "open-book" project. If you get stuck, simply reread this chapter to find the program statements you need and to see how they are used. There are many ways to write a program. If your program works, it's correct, even if it differs from the program given here. INPUT "How many numbers do you wish to average? ", howmany% IF howmany% <= 0 THEN PRINT "Not a valid quantity; must be greater than 0." ELSE total! = 0.0 ' Set running total to zero. FOR count% = 1 TO howmany% PRINT "number"; count%; INPUT " ", value! total! = total! + value! ' Add next value to total. NEXT count% PRINT "The average value is"; total! / howmany% END IF For More Information Now you know how to write simple programs in BASIC. There is, however, a great deal more to BASIC programming. QuickBASIC's manuals and on-line help provide complete information on using the QuickBASIC environment and each of the QuickBASIC statements and functions. However, the documentation does not include a complete introduction to BASIC, and does not teach the general principles of programming, or how to use DOS. The following books contain more information on those subjects. They are listed for your convenience only. With the exception of its own publications, Microsoft Corporation neither endorses these books nor recommends them over others on the same subjects. Books about BASIC Craig, John Clark. Microsoft QuickBASIC Programmer's Toolbox. Redmond, Wash.: Microsoft Press, 1988. Dwyer, Thomas A., and Margot Critchfield. BASIC and the Personal Computer. Reading, Mass.: Addison-Wesley Publishing Co., 1978. Enders, Bernd, and Bob Petersen. BASIC Primer for the IBM PC & XT. New York, N.Y.: New American Library, 1984. Feldman, Phil, and Tom Rugg. Using QuickBASIC 4. Carmel, Ind.: Que Corporation, 1988. Hergert, Douglas. Microsoft QuickBASIC. 2d ed. Redmond, Wash.: Microsoft Press, 1988 The first edition of this book discusses programming techniques appropriate for QuickBASIC Versions 2.0 and 3.0. Use the second edition for information on programming in QuickBASIC Version 4.0. Inman, Don, and Bob Albrecht. Using QuickBASIC. Berkeley, Cal.: Osborne McGraw-Hill, 1988. Books about DOS Duncan, Ray. Advanced MS-DOS. Redmond, Wash.: Microsoft Press, 1986. Wolverton, Van. Running MS-DOS. 2d ed. Redmond, Wash.: Microsoft Press, 1985. Wolverton, Van. Supercharging MS-DOS. Redmond, Wash.: Microsoft Press, 1986. ──────────────────────────────────────────────────────────────────────────── PART 2 HANDS ON WITH QUICKBASIC ──────────────────────────────────────────────────────────────────────────── Part 2, "Hands On with QuickBASIC" is a tutorial in which you finish a real application program, QCARDS.BAS. Although QCARDS is a model of good structured programming, the purpose of the tutorial is to introduce the Microsoft QuickBASIC environment, rather than teach programming techniques. The comments that describe each code block may be all you need to understand the programming, but you don't have to understand the programming concepts used in each section before moving on to the next. When you finish the tutorial, you will have used three of QuickBASIC's most sophisticated features──the smart editor, on-line help, and debugging──in real programming situations. Then you can review the program comments and code and use QuickBASIC's on-line help and debugging features to understand how each block works. Chapter 5 describes the structure of QCARDS, previews its interface, and shows you how to enter a SUB...END SUB procedure. In Chapter 6 you'll see how the smart editor helps catch and correct programming errors as you enter code. Chapters 7 and 8 give you practice in using on-line help the way you will use it while writing your own programs. In Chapter 9 you will track and fix a bug so QCARDS will run correctly. At the end of Chapter 9, QCARDS is fully functional and ready to use. ──────────────────────────────────────────────────────────────────────────── Chapter 5 The QCARDS Program This chapter describes QCARDS.BAS, the program on which the rest of the tutorial on QuickBASIC is based. You'll add some code in the form of a "procedure," a routine you write once and then call from different parts of the program, to perform a specific task. In this chapter, you will ■ Load a program at the same time you invoke QuickBASIC ■ Browse through the QCARDS.BAS code ■ Call procedures from the Immediate window ■ Create and call a SUB procedure This chapter takes about one hour to complete. Building QCARDS As you work through the QuickBASIC tutorial in Chapters 5-9, you'll add lines of code to the QCARDS program. The code-entry sequences that are part of QCARDS appear under special headings, so you know which ones are necessary for finishing the tutorial program. You can save your work as you finish each numbered sequence. If you make a mistake during a code-entry sequence, just reload the previous saved version and repeat the current sequence. ────────────────────────────────────────────────────────────────────────── NOTE As you browse through QCARDS, you may notice some errors in the code. These errors are intentional. You will fix them as you work through the tutorial. ────────────────────────────────────────────────────────────────────────── Loading a Program When You Start QuickBASIC You can start QuickBASIC and load a program at the same time by including the program name as a command-line "argument." An "argument" is information you supply to a command to modify the command. ────────────────────────────────────────────────────────────────────────── NOTE If you don't have a hard disk, copy the files QCARDS.BAS and QCARDS.DAT to an empty removable disk and use that disk to complete the tutorial. ────────────────────────────────────────────────────────────────────────── Type the following line at the DOS prompt to start QuickBASIC and have it automatically load QCARDS.BAS: qb qcards When you start QuickBASIC this way, QuickBASIC searches the current working directory for a file with the name QCARDS and the extension .BAS. If QuickBASIC finds the file, it loads it. If the file is not found, QuickBASIC assumes you are starting a new program that you want to name QCARDS.BAS. A Quick Tour of QCARDS If you completed the computer-based training called QB Express, you'll recognize some of QCARDS. In Chapters 5-9 you'll work with the real QCARDS code. If you are new to programming, some of this material may seem difficult because QCARDS is a real application program. Don't worry──you don't need to master all the material in each section before moving on. This tutorial is designed to teach the programming tools of the QuickBASIC environment, not programming techniques. Even if you have programmed in BASIC before, you may learn some powerful techniques because QCARDS is a structured program that uses procedures. In fact, if you have used a BASIC interpreter (like GW-BASIC(R) or BASICA), you're in for a pleasant surprise. The QCARDS Program QCARDS is a database program. It provides a convenient way to work with many small collections of information (called records), which are stored together in a disk file. QCARDS manages the disk file──opening and closing it and updating the records as you modify, add, or delete specific pieces of information or whole records. The fun part of QCARDS is the "interface," the part of the program where the user interacts with QCARDS (see Figure 5.1). ┌Records have fields │such as street and city QCARDS' help┐ ┌───────────┼──────────────────────────────────────────────────────────┼┐ │ │ ││ │ │ ││ │ ├─────────────────────────────────────┐ ││ │ ┌─┼───────────────────────────────────┐═╡ ┐ ││ │ ┌─┴─┼─────────────────────────────────┐═╡ │Select card with: │ ││ │ ┌─┴───┼───────────────────────────────┐═╡ │ │ UP │ ││ │ ┌─┌─┴─────┼─────────────────────────────┐═╡ │ │ │ DOWN │ ││ │ │ ╞═══════╪═════════════════════════════╡ │ │ │ │ PGUP ├─┘│ │ │ │Note: │_____________________________│ │ │ ├─┘ PGDN │ │ ┌─┼─│ │Birth: │__/__/__ Phone: ___-___-____│ │ ├─┘ HOME │ │ │ │ │ │Street:│\____________________________│ ├─┘ END │ │ │ │ │ │City: ___________ ST: ___ Zip: _____├─┘ ┘ │ │ │ └ └─────────────────────────────────────┘ │ │ │ ┐ │ │ │Edit Top Add New Copy to New Delete Find Sort Print Quit ├──┐ │ │ │ ┘ │ │ │ └───────────────────────────────────────────────────────────────────┼───┘ └──Each card represents a record. QCARDS' command line─┘ Figure 5.1 QCARDS' Interface QCARDS uses the concept of an index-card file to present the data in a familiar way. Each card that appears on screen represents a record in the database. Each card has several "fields" (separate areas on the card) that are used to enter new data or change and reorder existing data. Once you understand QCARDS, you can modify the data (and the program itself) and use it for any kind of information you wish to store. QCARDS is a large program, but it is organized according to structured programming principles (that is, it divides complicated tasks into simpler ones). This means you can learn its programming techniques gradually. As you read the next few sections, scroll down through QCARDS as each part is described. Declarations and Definitions QCARDS begins with a short section describing its purpose. Next comes a section of declarations and definitions. The declarations and definitions use statements like DEFINT, CONST, TYPE...END TYPE, DECLARE, DIM, and REDIM. They let QuickBASIC anticipate the amount of space to reserve in memory for the program's variables. For example,DEFINT A-Z tells QuickBASIC that any variable for which a data type is not explicitly declared should be considered an integer. CONST statements improve program readability by giving descriptive names to values the computer regards only as numbers. For example, the value 0 (zero) represents the logical condition "false" in QuickBASIC. At about line 45, a CONST statement defines the symbolic constant FALSE as the value zero. This lets you use the word FALSE to represent the value 0 in logical comparisons. TYPE...END TYPE constructions declare "aggregate" data types. Aggregate data types are those that can include both strings and all types of numeric values. For example, once the PERSON data type is declared (at about line 56), you can define variables to have this user-defined type. Lines that begin with the DECLARE statement allow QuickBASIC to check procedure calls to make sure you use them correctly. Comments After the declarations and definitions comes a large section that contains mostly comments. Each comment block describes a block of executable statements that you will enter as you complete QCARDS. The statements define the program's overall flow of control. This section of QCARDS concludes with an END statement to mark the end of the program's normal execution sequence. Statements Following the END Statement The final section of the program starts after the END statement. Each group of statements in this section is preceded by a "label," a name followed by a colon. (A QuickBASIC label is similar to line numbers in BASIC interpreters.) The statements associated with these labels are executed only if other statements (that contain references to the labels) are executed. The first label (MemoryErr) labels an error handler. If a certain type of error occurs during execution of QCARDS, the statements following MemoryErr display a message on the screen, then end the program. The remaining labeled sections contain DATA statements that are executed when the index cards are drawn on the screen. Calling QCARDS Procedures from the Immediate Window There are two levels of programming in QCARDS. The module level contains the program's most general logic. The procedure level contains many individual procedures that do the program's detailed work. Just as you can use the Immediate Window to see the effects of a BASIC statement, you can use it to call a program's procedures. This lets you see the effects of a procedure without running the entire program. Each procedure performs a specific task. The following steps illustrate how to call procedures that display the QCARDS user interface on the output screen: 1. Press F6 to move the cursor into the Immediate window. 2. Type CLS and press ENTER to clear the output screen. Then press a key to return the cursor to the Immediate window. 3. Type CALL DrawCards and press ENTER. QuickBASIC executes the DrawCards procedure. Calling a procedure is just like executing a BASIC statement. The procedure performs its task, then QuickBASIC waits for the next instruction. 4. Press a key to return to the Immediate window, then type the following on the next line in the Immediate window, exactly as shown: CALL ShowCmdLine : DO : LOOP 5. Press ENTER to execute the line you just typed. The ShowCmdLine procedure adds the QCARDS command line to the parts already displayed. This time, however, QuickBASIC does not immediately display the Press any key to continue prompt, because the DO and LOOP statements following ShowCmdLine create an unconditional loop (that is, an infinite loop). Breaking an Unconditional Loop from QCARDS While building QCARDS, you will need to escape from unconditional loops because QCARDS does not yet respond to key presses. However, QuickBASIC checks for one particular key-press combination, CTRL+BREAK, which lets you break out of an infinite loop and return to the QuickBASIC environment. Note that when you finish adding code to QCARDS, a user will be able to press any of the high-intensity letters on the QCARDS command line to execute commands. For example, the Q key will terminate the program and return control to QuickBASIC because QCARDS will check each key the user presses and carry out the requested action. Try this to break an unconditional loop: Press CTRL+BREAK to return control to QuickBASIC. Notice that when you press CTRL+BREAK, the cursor does not return to the Immediate window (where the last statement you executed is located). Instead, it is placed in the View window. The Module-Level Code Every QuickBASIC program has a module level──it's what QuickBASIC displays in the View window when you first open the program. Most of the code you will add to QCARDS is called "module-level code." It uses BASIC statements and functions (in combination with QCARDS procedures), to carry out the program's tasks, which are described in the comments. The module-level code you add to QCARDS defines the general way QCARDS interacts with the user. Structured Programming with Procedures You can write programs that have only a module level. However, the details of each task can obscure the general program logic, making the program difficult to understand, debug, and enhance. For ease of understanding and debugging, QCARDS delegates most processing tasks to procedures (such as DrawCards and ShowCmdLine) that are called when their tasks need to be performed. Figure 5.2 illustrates the relationship between module-level code and procedures and their execution sequences. ┌──────────────────────────────────────────────────────────────────────┐ ┌─│ PROGRAM.BAS Module │─ │ └──────────────────────────────────────────────────────────────────────┘ │ ┌───────────────────────────┐ ┌──────────────────────────────┐ │ ┌─│ Module-Level Code ├─┐ ┌─┤ Procedure-Level Code ├┐ │ │ └───────────────────────────┘ │ │ └──────────────────────────────┘│ │ │ │ │ │ │ │ (Definitions and declarations)│ │ │ │ │ ∙ │ │ │ │ │ ∙ │ │ │ │ │ ∙ │ │ │ │ │ (General execution sequence) \\ \\ │ │ │ ∙ │ │ │ ∙ │ │ │ ∙ ┌────────────────────────┐ │ │ │ CALL Procedure1 ════════════════════│SUB Procedure1 │ │ │ │ ∙═══════════════════════════════╗ │ ∙ │ │ │ │ ∙ ║ │ ∙ │ │ │ │ ∙ ║ │ ∙ │ │ │ │ Return Value=Procedure2═════╗ ║ │ReturnValue=Procedure2 ─┼─┐ │ │ │ ∙═══════════════════╗ ║ ║ │ ∙─────────────────────┼─┼──┐ │ │ │ ∙ ║ ║ ║ │ ∙ │ │ │ │ │ │ ∙ ║ ║ ║ │ ∙ │ │ │ │ │ │ ║ ║ ╚══│END SUB │ │ │ │ │ │ ║ ║ └────────────────────────┘ │ │ │ │ │ ║ ║ ┌────────────────────────┐ │ │ │ │ │ ║ ╚═══════│FUNCTION Procedure2 │┘ │ │ │ │ ║ │ ∙ │ │ │ │ │ ║ │ ∙ │ │ │ │ │ ║ │ ∙ │ │ │ │ │ ║ │Procedure2=returnval │ │ │ │ │ ║ │ ∙ │ │ │ │ │ ║ │ ∙ │ │ │ │ │ ║ │ ∙ │ │ │ │ │ ╚══════════════│END FUNCTION ───────────┼────┘ │ │ │ └────────────────────────┘ │ │ │ │ │ │ END // // ┌────────────────────────┐ │ │ │ (Error handlers and labeled │ │ │Any number of other SUB │ │ │ │ data) │ │ │and FUNCTION procedures │ │ │ │ ∙ │ │ │called from module-level│ │ │ │ ∙ │ │ │code and from each other│ │ │ │ ∙ │ │ └────────────────────────┘ │ │ │ │ │ │ │ └───────────────────────────────┘ └─────────────────────────────────┘ └────────────────────────────────────────────────────────────────────────── Figure 5.2 Modules and Procedures A procedure is usually a group of statements that performs a single task. Procedures are saved as part of the same disk file as the module-level code. However, QuickBASIC treats procedures as logically self-contained entities, separate from the module-level code and from each other. Although every program has a module level, a procedure level does not exist until a procedure is actually defined. QuickBASIC executes the statements in a procedure only if the procedure is explicitly invoked. You can invoke procedures from the module-level code, from other procedures, or from the Immediate window. A Profile of the Parts of the Program Even though they are all in the same disk file, QuickBASIC keeps a program's procedures separate from the module-level code and from each other. Therefore, you can't have a procedure and module-level code (or two procedures) in the same window at the same time. To edit these different parts of a program, you move them in and out of the View window using the View menu's SUBs command. The SUBs dialog box lists all the procedures in a program. Try the following to see a profile of all the parts of QCARDS: 1. Press ALT+V, then press S to choose the View menu's SUBs command. The SUBs dialog box lets you access all parts of your program (see Figure 5.3). The first entry, QCARDS.BAS, is a file name. It represents the program's module-level code. Name of module containing Procedures are indented procedures indented below it beneath module name. │ │ ┌┼───────────────────────────────── SUBs ───────────┼─────────────────── ││ │ ││Choose program item to edit │ ││┌─────────────────────────────────────────────────┼─────────────────── │└┼ QCARDS.BAS PrintLabel │ │ │ AsciiKey Prompt │ │ │ CleanUp SelectField │ │ │ ClearHelp ShowCards ──────────────┘ │ │ DrawCards ShowCmdLine │ │ EditCard ShowEditHelp │ │ EditString ShowTopCard │ │ FindCard ShowViewHelp │ │ InitIndex SortIndex │ └─▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ │┌QCARDS.BAS is the Main Module ││ ││ < Edit in Active > < Cancel > ├┼────────────────────────────────────────────────────────────────────── ││ < Delete > ───────────────────┐ < Help > └┼─────────────────────────────────┼──────────────────────────────────── │ │ Describes the Deletes a file from a program, selected item or a procedure from its file Figure 5.3 SUBs Dialog Box 2. Press DOWN to select the first entry beneath QCARDS.BAS. The first entry beneath QCARDS.BAS is AsciiKey. Each entry indented beneath QCARDS.BAS represents a SUB or FUNCTION procedure used by the program. All these procedures are saved in the QCARDS.BAS disk file. 3. Select the DrawCards procedure and press ENTER. QuickBASIC displays the code of the DrawCards procedure in the View window. Note that the View window's title bar contains QCARDS.BAS:DrawCards Use DIRECTION keys to scroll around in DrawCards. Its text is the only text in the View window. 4. Press ALT+V, then press S to choose the View Menu's SUBs command and select QCARDS.BAS if it is not already selected. 5. Press ENTER to return the module-level code to the View window. QuickBASIC lets you define two types of procedures: SUB and FUNCTION procedures. To include the code of a procedure in your program's execution sequence, place its name wherever you want its task performed. You invoke a SUB procedure by using its name in a CALL statement. FUNCTION procedures are used the way QuickBASIC's intrinsic functions (like TIME$) are. Procedures are an effective way to code tasks that are performed repeatedly. Defining a Procedure in QCARDS You can start learning about procedures by writing simple ones. Do the following to see how QuickBASIC automatically segregates each procedure from the rest of the program. It also shows you how to define and call a simple procedure that you'll use later in QCARDS. QCARDS Code Entry 1 1. Place the cursor at a blank line at the end of the declarations and definitions section in the View window (about line 102). 2. Press ENTER to create another blank line. 3. Type the words SUB Alarm and press ENTER. QuickBASIC opens a new window and starts the procedure with the statements SUB Alarm and END SUB. The statement DEFINT A-Z appears above the SUB statement because when you create a procedure, it inherits the default data type of the module-level code. The title bar in the View window now contains the name of the module (QCARDS.BAS) plus Alarm, the name of the procedure in the View window. 4. Type the following comment and code blocks, exactly as shown, between the SUB and END SUB statements: ' The Alarm procedure uses the SOUND statement to send signals ' to the computer's speaker and sound an alarm. ' ' ' Parameters: None ' ' Output: Sends an alarm to the user ' Change the numbers to vary the sound. FOR Tone = 600 TO 2000 STEP 40 SOUND Tone, Tone / 7000 NEXT Tone You can test the procedure and see what it does by calling it from the Immediate window. 5. Move the cursor to the Immediate window. Then type CALL Alarm and press ENTER. Saving Edited Text From now on, each time you save your work you will save the program with the name of the current chapter. When you save a program with a different name, the old version (QCARDS.BAS, in this case) still exists unchanged on disk. Therefore, if something makes a succeeding version of the program unusable, you can reload the previous version of the program and start over again. QCARDS Code Entry 2 1. Press ALT+F, then press A to choose the File menu's Save As command. The Save As dialog box appears (see Figure 5.4). ┌─Type your program name here │ ┌────────────────┼───── Save As ──────────────────┐ │ │ │ │ ┌──┴───────────────────────────────┐│ │ File Name: │ ││ │ └──────────────────────────────────┘│ │ C:\QB4.5\DEMO │ │ │ │ Dirs/Drives │ │ ┌──────────────┐ ┌─────── Format ────────┐ │ │ │.. │ (∙) QuickBASIC - │ │ │ │SOURCE ░ │ Fast Load and │ │ │ │[-A-] ░ │ Save │ │ │ │[-B-] ░ │ │ │ │ │[-C-] ░ │ ( ) Text - │ │ │ │[-U-] ░ │ Readable by │ │ │ │[-Z-] │ Other Programs │ │ │ └──────────────┘ └───────────────────────┘ │ ├─────────────────────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └─────────────────────────────────────────────────┘ Figure 5.4 Save As Dialog Box 2. Type the name chapter5 in the text box and press ENTER. This saves the program QCARDS.BAS as CHAPTER5.BAS on disk. The Alarm procedure that you created is saved as part of CHAPTER5.BAS. For More Information For more information on the topics covered in this chapter, see the following: Where to Look What You'll Find ────────────────────────────────────────────────────────────────────────── Chapter 11, "The File Menu" Complete information on file management in QuickBASIC, including file-format options and special commands for opening types of files other than single-file programs. Chapter 13, "The Edit Menu" and Complete information on creating and Chapter 14, "The View Menu" viewing procedures in QuickBASIC. Chapter 2, "SUB and FUNCTION Explanations of BASIC's rules for Procedures," in Programming in BASIC creating all types of SUB and FUNCTION procedures. ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 6 Editing in the View Window QuickBASIC's editing features let you write and modify programs quickly, easily and accurately. As you edit, QuickBASIC checks your code to make sure it is valid BASIC syntax. In this chapter you will use the editing tools to ■ Discover QuickBASIC's smart editor ■ Understand QuickBASIC's automatic text formatting ■ Use on-line help to answer questions on the spot ■ Use the Edit menu's Cut, Copy, and Paste commands ■ Search for and replace text You'll enter module-level code in QCARDS. If you have questions about any words you are typing, use on-line help (position the cursor on the word and press F1). On-line help includes complete descriptions and examples of each QuickBASIC statement and function. QuickBASIC also gives information on any variable, procedure, or symbolic constant at the cursor when you press F1. When you finish, press ESC to close the Help window. This chapter requires one to two hours to complete. The Smart Editor One thing that makes editing in QuickBASIC different from using an ordinary word processor is its "smart editor." QuickBASIC recognizes language keywords and warns you when they are being used incorrectly. QuickBASIC also inserts certain types of text into the program for you. For example, when you created the Alarm procedure in the last chapter, QuickBASIC inserted the DEFINT A-Z and END SUB statements for you when you entered the SUB Alarm statement. Automatic Formatting QuickBASIC's smart editor capitalizes keywords and places uniform spacing between operators (such as plus and minus signs) and their operands (the values they operate on). This makes your program easier to read. The following steps illustrate this: QCARDS Code Entry 3 1. Start QuickBASIC and open CHAPTER5.BAS (if it is not open). 2. Use PGDN and DOWN to move the cursor to the blank line beneath the following comment (at about line 106). Check the line counter on the reference bar to find the line. ' Open data file QCARDS.DAT for random access using file #1 3. Press ENTER to create a blank line, then type this statement exactly as shown, including the initial "comment delimiter" (the apostrophe preceding open): 'open "qcards.dat" for random as #1 len=len(card) 4. Press ENTER. QuickBASIC reads the line as though it were just a comment so no formatting is done. 5. Press UP to place the cursor at the comment delimiter. 6. Press DEL to delete the comment delimiter. 7. Press DOWN to move the cursor off the line. QuickBASIC converts the keywords (OPEN, FOR, RANDOM, AS, and LEN) to capital letters. Spaces are inserted on each side of the equal sign (=). Since it is easier to type in lowercase letters, lines of code are shown in this tutorial with keywords in lowercase. When you type them and press ENTER, QuickBASIC capitalizes the keywords for you. Words that aren't keywords (such as symbolic constants, procedure names, and variable names) appear in mixed case or all uppercase letters. The BASIC language is not "case sensitive." It doesn't distinguish between two versions of the same word by the case of the letters. For instance, the keyword OPEN is the same to the BASIC language as open or OpEn. When the smart editor capitalizes keywords, it is just for appearance. The variable name Card represents the same memory location as CArd or CaRD. The smart editor automatically maintains consistency in the capitalization of specific words in a program listing. Conventions used in this manual and QuickBASIC's handling of text you enter are summarized in the following list: Type of Word Appearance in QuickBASIC Action Manual ────────────────────────────────────────────────────────────────────────── BASIC keywords Lowercase Converts them to all uppercase letters when you enter the line Variable names and Mixed case Alters all instances of the name to procedure names most recent capitalization Symbolic constants Uppercase Changes all instances of the name to most recent capitalization ────────────────────────────────────────────────────────────────────────── The following steps illustrate the rules in the table above: QCARDS Code Entry 4 1. Move the cursor to the line below the following comment (at about line 113): ' To count records in file, divide the length of the file by the ' length of a single record; use integer division () instead of ' normal division (/). Assign the resulting value to LastCard. 2. Press ENTER to make space, then type the following line exactly as shown: LastCard=LoF(1)Len(Card) Note that the backslash (<|>) operator in BASIC performs integer division, rather than normal division. 3. Press ENTER. Keywords are capitalized and spaces are inserted. The previous capitalization of card (in the OPEN statement) is updated to Card, to conform to the way you just typed it. QuickBASIC assumes that the last way you entered the word in the View window is the way you want it everywhere. This is done to all occurrences of the word except those within comments. Syntax Checking When you move the cursor off any code line you edit (either by pressing ENTER or a DIRECTION key), QuickBASIC checks its syntax. If the line is not valid BASIC code, QuickBASIC displays a dialog box describing the error. The following steps show how the smart editor checks your code for syntax errors: QCARDS Code Entry 5 1. Move the cursor to the line beneath the following comment block (about line 130): ' Redefine the Index array to hold the records in the file plus ' 20 extra (the extra records allow the user to add cards). ' This array is dynamic - this means the number of elements ' in Index() varies depending on the size of the file. ' Also, Index() is a shared procedure, so it is available to ' all SUB and FUNCTION procedures in the program. ' ' Note that an error trap lets QCARDS terminate with an error ' message if the memory available is not sufficient. If no ' error is detected, the error trap is turned off following the ' REDIM statement. 2. Press ENTER, then type the following lines exactly as shown (including errors): on error goto MemoryErr redim shared Index(1 to LastCard + 20) as PERSOR on error goto 3. Press ENTER after the final line. QuickBASIC displays the following error message (see Figure 6.1): File Edit View Search Run Debug Calls Options Hel ┌────────────────────────────── CHAPTER5.BAS ─────────────────────────┤ │' Also, Index() is a shared procedure, so it is available to │' all SUB and FUNCTION procedures in the program. │ │ON ERROR GOTO MemoryErr │REDIM SHARED Index(1 TO LastCard + 20) AS PERSOR │ON ERROR GOTO ▓▓▓▓ │ ┌────────────────────────────────────────┐ │ │ │' Note that an err│ │or │' message if the m│ Expected: 0 or label or line number │ │' error is detecte│ │ the │' REDIM statement.├────────────────────────────────────────┤ │ │ < OK > < Help > │ │' Use the block IF└────────────────────────────────────────┘r │' to load the records from the disk file QCARDS.DAT into the │' array of records called Index() declared earlier. In the IF │' part, you will check to see if there are actually records │' in the file. If there are, LastCard will be greater than 0. │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> CN 00126: Figure 6.1 Error-Message Dialog Box When you use ON ERROR GOTO to turn off an error trap (as is being done here) QuickBASIC expects it to be followed by the number 0. 4. Press ESC to clear the dialog box. QuickBASIC places the cursor at the place the error was detected. 5. Add a zero at the end of the line so it looks like this: ON ERROR GOTO 0 Once you close an error-message dialog box, QuickBASIC doesn't check that statement's syntax again until you actually change the line. If you don't edit the line at all, QuickBASIC waits until you run the program before reminding you that the error still exists. Errors Detected When You Run Your Program Some errors are not apparent until you actually try to run your code. For example, in the REDIM statement you declared the Index() array as type PERSOR. This was a misspelling of the name of the user-defined type, PERSON, which you saw when you scrolled through the declarations and definitions section of QCARDS in Chapter 5 "The QCARDS Program." QuickBASIC did not detect this error on entry because it assumes that the PERSOR type is declared somewhere, even though it has not yet encountered the declaration. The following step illustrates how these errors are detected: Press ALT+R, then press S to choose the Run menu's Start command to run the lines entered so far. QuickBASIC displays the error message Type not defined and highlights the AS in the REDIM statement as shown in Figure 6.2. File Edit View Search Run Debug Calls Options Help ┌────────────────────────────── CHAPTER5.BAS ─────────────────────────┤├── │' Also, Index() is a shared procedure, so it is available to │' all SUB and FUNCTION procedures in the program. │ │ON ERROR GOTO MemoryErr │REDIM SHARED Index(1 TO LastCard + 20) AS PERSOR │ON ERROR GOTO 0 │ │' Note that an error trap ┌────────────────────────┐h an error │' message if the memory av│ │. If no │' error is detected, the e│ Type not defined │ollowing the │' REDIM statement. │ │ │ ├────────────────────────┤ │ │ < OK > < Help > │ │' Use the block IF...THEN.└────────────────────────┘e whether │' to load the records from the disk file QCARDS.DAT into the │' array of records called Index() declared earlier. In the IF │' part, you will check to see if there are actually records │' in the file. If there are, LastCard will be greater than 0. │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── │ │ <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> CN 00124:040 Figure 6.2 Error Message Help for Error Messages Error-message dialog boxes contain a Help button you can choose to get either a description of common causes for the error or the correct syntax plus examples of usage. 1. Press F1 to get on-line help for this error message, then choose the Help button in the dialog box. The following dialog box appears (see Figure 6.3): File Edit View Search Run Debug Calls Options Hel ┌────────────────────────────── CHAPTER5.BAS ─────────────────────────┤ │' Also, Index() is a shared procedure, so it is available to │' all SUB and FUNCTION procedures in the program. │ │ON ERROR GOTO MemoryErr │REDIM SHARED Index(1 TO LastCard + 20) AS PERSOR │ON ER┌────────────────────────────────────────────────────────────────┐ │ │ ┌────────────────────────────────────────────────────────────┐ │ │' Not│ │ No TYPE...END TYPE statement exists in this module for the │ │ │' mes│ │ user-defined type. │ │ │' err│ │ ■ Did you misspell the user-defined type name? │ │ │' RED│ │ ■ You can use the QuickBASIC Find command to locate all │ │ │ │ │ │ │ │ │ └────────────────────────────────────────────────────────────┘ │ │' Use├────────────────────────────────────────────────────────────────┤ │' to │ < OK > │ │' arr└────────────────────────────────────────────────────────────────┘ │' part, you will check to see if there are actually records │' in the file. If there are, LastCard will be greater than 0. │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ F1=Help Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item Figure 6.3 Help on Error Message The new dialog box indicates that no TYPE...END TYPE statement was found for PERSOR. 2. Press ESC as many times as necessary to clear the dialog boxes. Overtyping the Error Overtyping replaces the text at the cursor and moves the cursor right. Correct the error by overtyping, as follows: QCARDS Code Entry 6 1. Place the cursor on the second R in PERSOR. 2. Press INS to change from insert to overtype. The INS key is a "toggle." It changes the shape of the cursor from the default (a thin blinking line) to a blinking box. When the cursor is a thin line, text you type is inserted at the cursor position. When the cursor has the box shape, whatever you type "overtypes" (replaces) the text at the current cursor position. 3. Overtype the second R in PERSOR with an N so the line looks like this: REDIM SHARED Index(1 TO LastCard + 20) AS PERSON 4. Press INS to reset the toggle to its default (the thin line). 5. Type the following on the next blank line to call your Alarm procedure: call Alarm 6. Press ALT+R, then press S to choose the Run menu's Start command to run the lines. QCARDS doesn't produce any visible output yet, but Alarm produces its sound. 7. Press a key to return to the QuickBASIC environment. Automatic Procedure Declarations When QuickBASIC encounters a procedure invocation in a program, it creates the DECLARE statement automatically. Then, it writes the declaration at the first line of the file (when you save your program). The following steps illustrate this: QCARDS Code Entry 7 1. Press CTRL+HOME to move the cursor to the beginning of the program. 2. Press ALT+F, then press A to choose the File menu's Save As command. The Save As dialog box appears. 3. Type chapter6 in the text box, then press ENTER to save the program as CHAPTER6.BAS. QuickBASIC inserts the declaration on the first line of the program, as follows : DECLARE SUB Alarm() This is a good point to take a break. In the next section you'll move the declaration just created and change some of the existing QCARDS code. Working with Selected Text Blocks "Selecting" is the way you highlight a block of text to work with. To select a text block directly, place the cursor at the beginning of a block, then hold down the SHIFT key while pressing the appropriate DIRECTION key. Try the following to select a block of text: QCARDS Code Entry 8 1. Start QuickBASIC (if you exited when you took a break) and open CHAPTER6.BAS. 2. Press CTRL+HOME to make sure the cursor is at the program's first line. The line should be DECLARE SUB Alarm(). 3. Press SHIFT+DOWN to select this line. The only way you can remove the highlight from selected text and return it to its unselected state is by pressing one of the DIRECTION keys ( UP, DOWN, LEFT, RIGHT), or by pressing F6 to move to a different window. ────────────────────────────────────────────────────────────────────────── WARNING Be cautious with selected text! If you type any character (even the SPACEBAR) while a line of text is selected, whatever you type replaces all selected text in the active window. The text that was selected is then permanently lost. ────────────────────────────────────────────────────────────────────────── Cutting or Copying Selected Text The Edit menu has commands that let you move a block of selected text to and from a "Clipboard" (a dedicated space in memory). The Cut and Copy commands put selected text on the Clipboard. The Paste command copies whatever text is on the Clipboard to the current cursor position. If a line (or more) of text is selected in the active window when you choose the Paste command, the text on the Clipboard replaces the selected text. When a menu command is available, it is marked with a high-intensity letter. For example, if you open the Edit menu now, the Cut and Copy commands are available because there is text selected in the active window. However, the Paste command is not available unless you have already placed text on the Clipboard. The following steps use the Cut command to transfer the text from its current position to the Clipboard: QCARDS Code Entry 9 1. Select the line DECLARE SUB Alarm if it isn't already selected. 2. Press ALT+E to open the Edit menu if it is not already open. 3. Press T to choose the Cut command. The selected text is transferred to the Clipboard. You can only copy one block at a time to the Clipboard because each new block (regardless of its size) replaces everything that preceded it on the Clipboard. ────────────────────────────────────────────────────────────────────────── IMPORTANT The shortcut-key combination for Cut is SHIFT+DEL. If you just press DEL while text is selected, it is deleted, but not to the Clipboard. You cannot recover text deleted with DEL. ────────────────────────────────────────────────────────────────────────── The Copy command is similar to Cut, but it puts a duplicate of the selected text on the Clipboard and leaves the selected block as is. ────────────────────────────────────────────────────────────────────────── NOTE Copy leaves the original text block selected, so you have to press a DIRECTION key before typing anything or the block will be replaced by what you type. ────────────────────────────────────────────────────────────────────────── Pasting a Text Block Any text you put on the Clipboard remains there until you either put something else on the Clipboard or until you exit from QuickBASIC. Follow these steps to move to the procedure-declarations section of QCARDS and paste in the declaration for Alarm: QCARDS Code Entry 10 1. Press ALT+S, then press F to choose the Search menu's Find command. The Find dialog box appears (see Figure 6.4). ┌─────────────────────────Find────────────────────────────────┐ │ ┌─────────────────────────────────────────────┐ │ │ Find What: │ │ │ │ └─────────────────────────────────────────────┘ │ │ │ │ ┌────────Search─────────────┐ │ │ [ ] Match Upper/Lowercase │( ) 1. Active Window │ │ │ [ ] Whole Word │(∙) 2. Current Module │ │ │ │( ) 3. All Modules │ │ │ └───────────────────────────┘ │ │ │ ├─────────────────────────────────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └─────────────────────────────────────────────────────────────┘ Figure 6.4 Find Dialog Box 2. Type the following line in the text box: This space reserved 3. Press ENTER to start the search. 4. Press HOME to place the cursor in column 1. 5. Press SHIFT+END to select the whole line. 6. Press ALT+E, then press P to choose the Edit menu's Paste command. The Paste command is active because there is text on the Clipboard. The text from the Clipboard replaces the selected text. 7. Save the program as CHAPTER6.BAS. Manipulating Selected Text You can manipulate selected text in other ways. For instance, you can indent selected text as a block rather than one line at a time. The following steps illustrate this: QCARDS Code Entry 11 1. Press ALT+S, then press F to choose the Search menu's Find command. Type the following line in the text box, exactly as shown: ' Define temporary There may be text selected in the text box when the dialog box opens. If so, whatever you type replaces the selected text automatically. You can remove the selection from the text by pressing a DIRECTION key if you want to just change the text in the box rather than completely replacing it. 2. Press ENTER. The cursor should move to the following line: ' Define temporary Index() array to illustrate QCARDS screen 3. Press SHIFT+DOWN twice so both the following lines are selected: ' Define temporary Index() array to illustrate QCARDS screen REDIM SHARED Index(1) AS PERSON 4. Press TAB while this text block is selected. The whole block moves right by one tab stop. 5. Press SHIFT+TAB to move the block left by one indentation level. 6. Press DEL to delete the entire block permanently. 7. Save the program as usual as CHAPTER6.BAS. Note that the text you just deleted was not placed on the Clipboard. This is because you deleted it with DEL rather than SHIFT+DEL (the shortcut key for the Cut command). The temporary Index() array definition is no longer needed because you defined it (with a REDIM statement) in the first part of this chapter. Searching and Replacing Text ──────────────────────────────────────────────────────────────────────────── IMPORTANT The remaining sections of this chapter provide practice using QuickBASIC's search and replace feature. The code you enter in the optional code-entry sections below is not necessary to make QCARDS run. You may want to read the rest of the chapter before deciding whether to try the optional code-entry sequences. If you make a mistake entering any of the optional sequences, the final program won't run properly. If you choose to do any of the optional code-entry sequences, you must do all three of them. ──────────────────────────────────────────────────────────────────────────── In this section, you'll define the symbolic constant DISKFILE$ to represent "QCARDS.DAT" the name of the disk file that contains QCARDS' data. Then you'll use the Search menu's Change command to replace all instances of the text string "QCARDS.DAT" with the symbolic constant. Once you define the constant DISKFILE$, you can just change the definition of DISKFILE$ if you want to load a different data file in QCARDS (or create a new data file). Defining the Symbolic Constant The first thing to do is define the constant. There is already an appropriate place to do this in the declarations and definitions section. Do the following to find the place and then add the constant: Optional QCARDS Code Entry 1 1. Save CHAPTER6.BAS as OPTIONAL.BAS. This way, if you do everything right you can start the next chapter by loading OPTIONAL.BAS, then saving it as CHAPTER7.BAS. If you make an error in one of the optional sections and find you can't correct it, you can start with CHAPTER6.BAS in the next chapter. 2. Press CTRL+HOME to move to the beginning of QCARDS. 3. Press ALT+S, then press F to choose the Search menu's Find command. Finally, type the following in the text box: TMPFILE 4. Press ENTER to place the cursor at the definition of TMPFILE. It looks like this: CONST TMPFILE$ = "$$$87y$.$5$" ' Unlikely file name 5. Press DOWN to remove selection from TMPFILE. 6. Press HOME to place the cursor in the leftmost column, then type the following line, exactly as shown, but don't press ENTER: const DISKFILE$ = "QCARDS.DAT" 7. Press SHIFT+LEFT until the string "QCARDS.DAT" is completely selected. Be sure both quotation marks are included in the selection. It's important to make sure the quotation marks are selected because you want to replace "QCARDS.DAT" with DISKFILE$. Replacing Multiple Occurrences of Text Using the Change command is much like the Find command, except that QuickBASIC lets you substitute specified text when matching text is found before it searches for the next match. Next you will change "QCARDS.DAT" to DISKFILE$ everywhere except in the definition you wrote in the last section. The Search menu's Change command lets you automate the process. Optional QCARDS Code Entry 2 1. Press ALT+S, then press C to choose the Search menu's Change command. The Change dialog box's Change command appears (see Figure 6.5): Text you want to This text will replace the │change goes here. │text you want to change. ┌─────────────┼─────────────────────┼───────────────────────────┐ │ ┌┼─────────────────────┼────────────────────────┐ │ │ Find What: │"QCARDS.DAT" │ │ │ │ └──────────────────────┼────────────────────────┘ │ │ ┌──────────────────────┼────────────────────────┐ │ │ Change To: │DISKFILE$ │ │ │ └───────────────────────────────────────────────┘ │ │ │ │ │ │ [ ] Match Upper/Lowercase │ │ [ ] Whole Word │ │ │ ├───────────────────────────────────────────────────────────────┤ │ < Find and Verify > < Change All > <Cancel > < Help > │ └───────────────────────────────────────────────────────────────┘ Figure 6.5 Change Dialog Box Because "QCARDS.DAT" is selected in the View window, the Find What text box has"QCARDS.DAT"in it. 2. Press TAB to move the cursor to the Change To text box. This is where you enter the text you want to substitute for the search text. 3. Type DISKFILE$ in this text box. 4. Press ENTER to choose the Find and Verify command button (the default). ────────────────────────────────────────────────────────────────────────── WARNING The second command button, Change All, makes all the changes without showing you the occurrences or waiting for confirmation. This option is risky unless you are sure you want to change all the occurrences. Even then, you may inadvertently change words that contain the search text in a way you didn't anticipate. If you have any doubts, use the default option Find and Verify. The Cancel button or ESC aborts the search and replace operation entirely. ────────────────────────────────────────────────────────────────────────── The Find and Verify command button highlights each occurrence of the search text, then displays the Change, Skip, Cancel dialog box (see Figure 6.6). In the next section you'll use it to make selective replacements. It contains buttons you can choose when you decide whether to replace the current occurrence: ┌───────────────────────────Change──────────────────────────────┐ │ │ ├───────────────────────────────────────────────────────────────┤ │ < Change > < Skip > < Cancel > < Help > │ └───────────────────────────────────────────────────────────────┘ Figure 6.6 Change, Skip, Cancel Dialog Box The Change, Skip, Cancel dialog box should still be on your screen. Replace occurrences of "QCARDS.DAT" with DISKFILE$ as follows: Optional QCARDS Code Entry 3 1. Press C to change the first occurrence. It is in the OPEN statement you entered earlier in this chapter. QuickBASIC moves to the next match. It is in a comment line in the CleanUp procedure (check the View window's title bar). 2. Press C to make the change. QuickBASIC moves to the next match. It is also in CleanUp in the line KILL "QCARDS.DAT" 3. Press C to make the change. QuickBASIC moves to the next match. It is also in CleanUp in the line NAME TMPFILE AS "QCARDS.DAT" 4. Press C to make the change. QuickBASIC moves to the next match. It is in a different procedure, InitIndex, in a comment line. 5. Press C to make the change. The final match is at CONST DISKFILE$ = "QCARDS.DAT" where you started. You don't want to change this one because this definition is the reason you just made all the other changes. 6. Press S to choose the Skip command button. When all occurrences have either been changed or skipped, QuickBASIC displays a dialog box containing ChangeComplete. 7. Press ESC to close the dialog box. Checking Your Work Whenever you make a series of changes throughout a program, you should check your work by running the program. If you've made a mistake during editing, you can use QuickBASIC's error messages to help you track down mistakes. Finish this session with the following procedure: 1. Press ALT+R, then press S to choose the Run menu's Start command to run the lines. If you get an error message, try to track down the error and fix it before you end the session. Go back over each of the optional QCARDS code-entry sections and compare your work with them. 2. Press a key to return to the QuickBASIC environment. 3. Save the program. If you renamed it OPTIONAL.BAS, you can just start with that file in the next chapter and rename it CHAPTER7.BAS. The constant DISKFILE$ now represents QCARDS.DAT in the program. Later you may want to modify the program to allow the user to load different files while the program is running. If you do, you can't represent the the file with the constant DISKFILE$, because the point of a constant is that it cannot be changed when the program is running. You would have to remove the CONST part of the definition and just make DISKFILE$ an ordinary string variable. For More Information For more information on the topics covered in this chapter, see the following: Chapter Topic ────────────────────────────────────────────────────────────────────────── Chapter 12, "Using the Complete information on QuickBASIC's editing Editor," and Chapter features, including the commands found on Full 13, "The Edit Menu" Menus and editing shortcut-key combinations Chapter 2, "SUB and Defining and using procedures and placement of FUNCTION Procedures," automatically generated procedure declarations. in Programming in BASIC Chapter 4, "String Using strings as symbolic constants Processing," in Programming in Basic Chapter 6, "Error and Using the ON ERROR statement Event Trapping," in Programming in BASIC ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 7 Programming with On-Line Help You've seen Microsoft QuickBASIC's on-line help features in previous chapters. In this chapter you'll use on-line help to guide you in writing some code for the QCARDS program. You will ■ Use alternative methods to get on-line help for QuickBASIC keywords ■ Access information about on-line program symbols through help ■ Use hyperlinks to get additional information within the Help window This chapter takes about one hour to complete. Using On-Line Help to Construct Statements In this section you'll use the Help menu's Index command to find out how to use statements. Do this first: QCARDS Code Entry 12 1. Start QuickBASIC if it is not running and open CHAPTER6.BAS (or OPTIONAL.BAS, whichever is appropriate). 2. Save the program immediately as CHAPTER7.BAS. On-Line Help for Keywords If you know the statement you want to use, you can find it quickly by choosing the Index command from the Help menu. You can get information on the first code block you'll enter in this chapter (the IF...THEN...ELSE statement) by doing the following steps: 1. Choose the Help menu's Index command (press ALT+H, then press I). Index lists all the QuickBASIC keywords. Scroll down through the list to see what it contains (use DIRECTION keys), or press the initial letter of the keyword you want more information on. 2. Select IF... THEN (press I). QuickBASIC places the cursor in the IF...THEN statement 3. Get help on IF..THEN (press F1). A QuickSCREEN appears (see Figure 7.1). It includes a brief description of the statement, the syntax for the block form of IF...THEN...ELSE, and a description of the terms used in the block. Syntax block │ │ File Edit View Search Run Debug Calls Options Hel ┌┼────────────── HELP: IF...THEN...ELSE Statement QuickSCREEN ────────┤ ││ QuickSCREEN Details Example Contents Index │├────────────────────────────────────────────────────────────────────── │IF...THEN...ELSE - a control flow statement that allows conditional ││ execution or branching, based on the evaluation of ││ an expression that must be either true or false ││ │Block IF...THEN...ELSE Syntax ││┌IF booleanexpression1 THEN │││ [statementblock-1] │││[ELSEIF booleanexpression2 THEN │└┤ [statementblock-2] │ │. . . │ │[ELSE │ │ [statementblock-n]] │ └END IF │ │ ■ booleanexpression is an expression that must return non-zero (true) │ or zero (false) │ ■ statementblock consists of any number of statements on one or more │ lines. │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ <Shift+F1=Help> <F6=Window> <Esc=Cancel> <Ctrl+F1=Next> <Alt+F1=Back> Figure 7.1 QuickSCREEN for IF...THEN...ELSE Statement 4. Make the Help window fill the whole screen (press CTRL+F10). 5. Move down to the syntax for the single-line form of IF...THEN...ELSE (press PGDN). 6. Move the cursor back to the top of the QuickSCREEN (press CTRL+HOME). 7. Restore the View and Immediate windows (press CTRL+F10). If you've used the statement before, the QuickSCREEN help information is usually sufficient to help you write your code. Hyperlinks in On-Line Help The QuickSCREEN includes four hyperlinks across the top. You can move the cursor to any one by pressing the TAB key or the initial letter of the word in the hyperlink. The following list describes what is displayed by each of the hyperlinks: Hyperlink Information Displayed by Help ────────────────────────────────────────────────────────────────────────── Details Gives full explanation of each syntax element and describes all ways of using the statement Example Shows code examples that illustrate syntax use Contents Shows all possible categories of on-line help available in QuickBASIC Index Lists QuickBASIC keywords alphabetically ────────────────────────────────────────────────────────────────────────── Try each of the available hyperlinks in turn, pressing ALT+F1 each time to return to the original syntax screen. If you keep choosing several hyperlinks without returning to the previous screen, you can work your way backwards through the hyperlink sequence by pressing ALT+F1 repeatedly (up to a limit of 20 links). Although you can't type in the Help window, you can size it with ALT+PLUS and ALT+MINUS so that the information you need is displayed while you enter text in the View window. When you understand the block IF...THEN...ELSE statement, implement the programming described in the comment block as follows: QCARDS Code Entry 13 1. Place the cursor in the View window (press F6). 2. Scroll down to the line beneath the following comment block (about line 145) and create a line of space (press ENTER): ' Use the block IF...THEN...ELSE statement to decide whether ' to load the records from the disk file QCARDS.DAT into the ' array of records called Index() declared earlier. In the IF ' part, you will check to see if there are actually records ' in the file. If there are, LastCard will be greater than 0 ' and you can call the InitIndex procedure to load the records ' into Index(). LastCard is 0 if there are no records in the ' file yet. If there are no records in the file, the ELSE ' clause is executed. The code between ELSE and END IF starts ' the Index() array at card 1. 3. Type the following code, exactly as shown: if LastCard <> 0 then call InitIndex(LastCard) else Card.CardNum = 1 Index(1) = Card put #1, 1, Card end if 4. Save the program as CHAPTER7.BAS. Then place the cursor back on the ELSE keyword. 5. Run your program up to the line on which the cursor rests (press F7). The line at the cursor appears in high-intensity video with the colors you chose for the Current Statement option in the Options menu's Display dialog box. This means that the program is still running, but execution is temporarily suspended. On-Line Help for Program Symbols QuickBASIC provides help for all "symbols" in your program. A symbol is anything that is defined, either explicitly or implicitly. For example, QuickBASIC keywords are symbols defined by the language. To get help for the symbols you define in your programs, place the cursor anywhere in the symbol, then press F1. QuickBASIC displays all the information it has about the symbol and where it is used in the program. Try this to find out about Card.CardNum. 1. Place the cursor in the word CardNum in Card.CardNum and press F1. The Help window shown in Figure 7.2 appears. File Edit View Search Run Debug Calls Options Hel ┌───────────────────────────── HELP: CardNum ─────────────────────────┤ │CardNum is a symbol that is used in your program as follows: │ │┌ C:\QB4.5\DEMO\DIR1\CHAPTER7.BAS ──── ││ An element of a user defined TYPE: ││ TYPE PERSON ││ CardNum AS INTEGER ││ Names AS STRING * 37 ││ Note AS STRING * 31 ││ Month AS INTEGER ││ Day AS INTEGER ││ Year AS INTEGER ││ Phone AS STRING * 12 ││ Street AS STRING * 29 ││ City AS STRING * 13 ││ State AS STRING * 2 ││ Zip AS STRING * 5 ││ END TYPE ││ │ ├────────────────────────────── CHAPTER7.BAS ─────────────────────────┤ │ Card.CardNum = 1 ├─────────────────────────────── Immediate ───────────────────────────── <Shift+F1=Help> <F5=Continue> <F9=Toggle Bkpt> <F8=Step> 00144: Figure 7.2 Symbol Help for CardNum On-line help describes CardNum as an element of the PERSON user-defined type. The help displays the actual TYPE...END TYPE statement. CardNum is the first element. 2. Move the cursor to the left until it is in the word Card on the left side of the period, then press F1. On-line help shows that the name Card is used many places in QCARDS. The specific instance at the cursor when you pressed F1 is described first; it is described as a variable of type PERSON. Note that in several procedures, Card is also used as a variable name, but is a variable of type INTEGER. Also, Card is sometimes described as a parameter of type PERSON. On-line help makes it easy to track the use of variable names throughout your programs. Although on-line help doesn't include the current value of a variable, QuickBASIC makes it easy to determine the current value of a variable in a suspended program. Here's how: 1. Close the Help window (press ESC). 2. Place the cursor anywhere in the word LastCard (about line 150). 3. Choose the Debug menu's Instant Watch command. QuickBASIC displays the Instant Watch dialog box (see Figure 7.3). It contains the name of the variable LastCard and its current value. (The actual value reflects the number of records in the QCARDS.DAT data file.) File Edit View Search Run Debug Calls Options Hel ┌────────────────────────────── CHAPTER7.BAS ─────────────────────────┤ │ CALL InitIndex(LastCard) │ELSE │ Card.CardNum = 1 │ Index(1) = Card │ PUT #1, 1.┌─────────────────────────────────────────────┐ │ENDIF │ │ │ │ ┌───────────── Expression ──────────────┐ │ │ │ │LastCard │ │ │' Use the Draw│ └───────────────────────────────────────┘ │ │' and draw the│ │ │' card. Finall│ ┌──────────────── Value ────────────────┐ │ │' as arguments│ │ 16 │ │ │' ShowCards pl│ └───────────────────────────────────────┘ │ │' card on the ├─────────────────────────────────────────────┤ │' information │ < Add Watch > < Cancel > < Help > │ │ └─────────────────────────────────────────────┘ │ │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ F1=Help Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item Figure 7.3 Instant Watch Dialog Box 4. Clear the Instant Watch dialog box (press ESC). Perform the following steps to place the QCARDS cards on the screen and the data from QCARDS.DAT on the cards: QCARDS Code Entry 14 1. Place the cursor on the line beneath the following comment (about line 163): ' Use the DrawCards procedure to initialize the screen ' and draw the cards. Then, set the first card as the top ' card. Finally, pass the variables TopCard and LastCard ' as arguments to the ShowCards procedure. The call to ' ShowCards places all the data for TopCard on the front ' card on the screen, then it places the top-line ' information (the person's name) on the remaining cards. 2. Create a line of space (press ENTER), then type the following code lines exactly as shown: call DrawCards TopCard = 1 call ShowCards(TopCard, LastCard) 3. Place the cursor back on the last line you entered (the one beginning withCALL ShowCards). 4. Execute the program to the line at the cursor (press F7). 5. Choose the View menu's Output Screen command to toggle back and forth between the QuickBASIC environment and the QCARDS output screen (press F4). You can use the same techniques as before to get help for the CALL keyword that transfers control to a BASIC SUB procedure. You can also get help for the DrawCards and ShowCards procedures and for the variable named TopCard. Since the program is still running (though suspended) you can also check the values of its variables using the Debug menu's Instant Watch command. Printing Screens from On-Line Help The Print command on the File menu can make hard copies of text from on-line help. If you have a printer connected to the parallel port, you can print hard copy of any of the help screens as follows: 1. Choose the Help menu's Index command and move the cursor to the DO...LOOP statement entry. Then move that statement's on-line help into the Help window (press F1). 2. Choose the File menu's Print command (press ALT+F, then press P). When the Help window is the active window, you can choose the option to print either specifically selected text or the whole current help screen (see Figure 7.4). File Edit View Search Run Debug Calls Options Hel ┌────────────────── HELP: DO...LOOP Statement QuickSCREEN ────────────┤ │ QuickSCREEN Details Example Contents Index │─────────────────────────────────────────────────────────────────────── │DO...LOOP - a control flow statement that repeats a block of statements │while a condition is true or until a condition becomes true │ │Syntax 1 ┌────────── Print ───────────┐ │ DO [{WHILE | UNTIL} b│ │ │ [statementblock] │ ( ) Selected Text │ │ LOOP │ (∙) Active Window │ │ │ │ │Syntax 2 │ │ │ DO │ │ │ [statementblock] ├────────────────────────────┤ │ LOOP [{WHILE | UNTIL}│ < OK > < Cancel > < Help > │ │ └────────────────────────────┘ │ ■ booleanexpression is an expression that will return non-zero (true) │ or zero (false). │ ■ statementblock is any number of statements on one or more lines whi │ are to be executed as long as booleanexpression is true. │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├───────────────────────────── CHAPTER7.BAS ──────────────────────────┤ ├─────────────────────────────── Immediate ───────────────────────────── F1=Help Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item Figure 7.4 Print Dialog Box (Help) 3. Print this help screen if you have a printer (press ENTER), otherwise clear the dialog box (press ESC). (If you try to print when you don't have a printer, a Device unavailable dialog box may be displayed.) 4. Choose any hyperlinks you'd like to see, then print them out. 5. Close the Help window (press ESC). Use the hard copy of the help text (or on-line help) to understand the programming. In the next steps, you'll insert the unconditional loop. QCARDS Code Entry 15 1. Move the cursor to the line below this comment block (about line 178): ' Keep the picture on the screen forever with an unconditional ' DO...LOOP statement. The DO part of the statement goes on ' the next code line. The LOOP part goes just before the END ' statement. This loop encloses the central logic that lets ' a user interact with QCARDS. 2. Create a blank line (press ENTER). 3. Type the word do then press ENTER. 4. Move the cursor down to the line beneath this comment (at about line 226): ' This is the bottom of the unconditional DO loop. 5. Create a blank line (press ENTER), then type the word loop 6. Choose Run menu's Start command. You will need to break out of this unconditional DO loop. 7. Press CTRL+BREAK when you want to suspend execution of the unconditional DO loop. While execution is suspended, you can use commands like Instant Watch to examine the variables. Afterwards, you can continue program execution by choosing the Continue command from the Run menu (press ALT+R, then press N). 8. Save the program as CHAPTER7.BAS. For More Information For more information on on-line help, see the following: Chapter Topic ────────────────────────────────────────────────────────────────────────── Section 10.8, "Using Information on QuickBASIC's Help menu commands On-Line Help" and and complete descriptions of all the Help Chapter 21, "The Help features Menu" ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 8 Using Example Code from On-Line Help You've seen many facets of Microsoft QuickBASIC's on-line help in previous chapters. Each QuickSCREEN and Details screen for each statement and function contains a hyperlink to one or more code examples. In this chapter you will copy example code from on-line help to use in QCARDS. You'll use some of these examples as you ■ Copy example code from on-line help and paste it into the View window ■ Edit text copied from on-line help to work in a specific program This chapter takes about one to one and one-half hours to complete. Copying Example Code from On-Line Help When you use on-line help for keywords, the QuickSCREEN describes the action and syntax of the keyword. If you have used the statement before, the syntax block may give all the information you need to write your code. However, if the statement is new to you, the Details and Example screens clarify how to use the syntax. In the next several code-entry sequences, you'll find an example in on-line help that you can copy and use in QCARDS. Example code from on-line help may not be a perfect match for QCARDS. Some code that you copy conflicts with code in the program. Don't worry──you'll fix it later in the tutorial. QCARDS Code Entry 16 1. Place the cursor on the line following this comment block (about line 192): ' Get user keystroke with a conditional DO...LOOP statement. ' Within the loop, use the INKEY$ function to capture a user ' keystroke, which is then assigned to a string variable. The ' WHILE part of the LOOP line keeps testing the string ' variable. Until a key is pressed, INKEY$ keeps returning a ' null (that is a zero-length) string, represented by "". ' When a key is pressed, INKEY$ returns a string with a ' length greater than zero, and the loop terminates. 2. Create a blank line (press ENTER). Then, type do 3. Display the QuickSCREEN for the DO keyword (press F1). When you press F1 when the cursor is on a blank space, QuickBASIC displays context-sensitive help on the symbol at the left of the cursor. Note that the cursor remains in the View window. 4. Move the cursor into the Help window (press F6 twice). 5. Choose the Example hyperlink (press E, then press F1). The example screen appears in the Help window (see Figure 8.1): File Edit View Search Run Debug Calls Options Help ┌───────────── HELP: DO...LOOP Statement Programming Examples ────────┤├── │ QuickSCREEN Details Example Contents Index │───────────────────────────────────────────────────────────────────────── │DO...LOOP Statement Programming Examples │ │Following are four examples. The first two examples show you how │placement of the condition affects the number of times the block │of statements is executed. The third example shows how a loop │can be used to pause a program until the user presses a key. The │fourth example illustrates testing at the end of a loop and presents │a sort subprogram where an ending test is appropriate. │ │DO...LOOP Programming Example 1 │ │In the following example, the test is done at the beginning of the │loop. Because I is not less than 10, the body of the loop (the │statement block) is never executed. │ │' DO...LOOP with test at the top of the loop. │' Output shows that loop was not executed. │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├───────────────────────────── CHAPTER7.BAS ──────────────────────────┤├── ├─────────────────────────────── Immediate ──────────────────────────────── <Shift+F1=Help> <F6=Window> <Esc=Cancel> <Ctrl+F1=Next> <Alt+F1=Back> Figure 8.1 Example Screen for DO...LOOP Statement The first paragraph of the screen describes the examples below. The description of the third example corresponds closely to the task you want to code into QCARDS at this point. Follow these steps to place the example code on the Clipboard: QCARDS Code Entry 17 1. Scroll down to Example 3. It looks like this: ' DO...LOOP with test at the bottom of the loop. DO Choice$ = INKEY$ LOOP WHILE Choice$ = "" 2. Select all four of the above lines. 3. Choose the Copy command from the Edit menu to place the lines on the Clipboard (press ALT+E, then press C). 4. Close the Help window (press ESC). 5. Select the DO you typed into the View window just before moving to the Help window (press SHIFT+HOME). 6. Choose the Paste command from the Edit menu (press ALT+E, then press P). The text from the Clipboard replaces the text that was selected. 7. Choose the Run menu's Start command to check for errors (press ALT+R, then press S), then return to QuickBASIC (press CTRL+BREAK). You can use on-line help to check for potential conflicts between the code you just copied and QCARDS, as follows: 1. Place the cursor on Choice$ and press F1. 2. On-line help shows you that variables named Choice$ now occur twice in QCARDS, once in the module-level code and once in the EditString procedure. These don't conflict because variables local to a procedure are not known at the module level and vice versa. Indenting a Block of Code The loop you just entered is "nested" within the unconditional loop you entered earlier (in "QCARDS Code Entry 15," in Chapter 7, "Programming with On-Line Help"). This means that it is executed once each time the outer loop is executed. Nested code is usually indented one tab stop to the right of the code encompassing it to show visually the levels of nesting within your program. Here's a reminder of how to indent multiple text lines as a block: 1. Select the three code lines you just entered. They look like this: DO Choice$ = INKEY$ LOOP WHILE Choice$ = "" 2. Move the whole block right one tab stop (press TAB). 3. Remove the selection from the block (press any DIRECTION key). The rest of the code you enter in QCARDS is nested within the unconditional DO loop so each block should be similarly indented. Copying Large Code Blocks from On-Line Help The code you copied in the preceding section was short and simple. It contained only one variable name, so the likelihood of a conflict with an existing symbol in QCARDS was small. You can copy larger blocks of example code from on-line help and paste them into programs you write. However, the code you copy may conflict with code you've already written into your program. In this section you'll copy more example code into QCARDS, then customize it significantly. Some of it will conflict, but you'll fix it later. QCARDS Code Entry 18 1. Move the cursor to the line beneath the following comment block (about line 222): ' The ELSE clause is only executed if Choice$ is longer than a ' single character (and therefore not a command-line key). ' If Choice$ is not an ASCII key, it represents an "extended" ' key. (The extended keys include the DIRECTION keys on the ' numeric keypad, which is why QCARDS looks for them.) The ' RIGHT$ function is then used to trim away the extra byte, ' leaving a value that may correspond to one of the DIRECTION ' keys. Use a SELECT CASE construction to respond to those key- ' presses that represent numeric-keypad DIRECTION keys. 2. Create a blank line (press ENTER), then type select case Choice$ 3. Press HOME, then display help for the SELECT CASE statement (press F1). 4. The help screen shown in Figure 8.2 appears. File Edit View Search Run Debug Calls Options Help ┌─────────────────── HELP: SELECT Statement QuickSCREEN ──────────────┤├── │ QuickSCREEN Details Example Contents Index │───────────────────────────────────────────────────────────────────────── │SELECT CASE - a control flow statement that executes one of several │ statement blocks depending on the value of an expression │ │Syntax │ SELECT CASE textexpression │ [CASE expressionlist1] │ [statementblock-1] │ [CASE expressionlist2 │ [statementblock-2] ... │ │ [CASE ELSE │ [statementblock-n]] │ END SELECT │ │ ■ testexpression is any numeric or string expression. │ ■ expressionlist contains one or more expressions of the same type as │ testexpression ├───────────────────────────── CHAPTER7.BAS ──────────────────────────┤├── │ SELECT CASE Choice$ ├─────────────────────────────── Immediate ──────────────────────────────── <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> 00214:013 Figure 8.2 QuickSCREEN for SELECT CASE Statement The SELECT CASE statement is commonly used like a switchboard in situations where there are numerous possible inputs, and many of them must be handled in unique ways. You don't want to take a unique action for each key a user might press, but with this kind of structure you can add CASE clauses for each key you want to handle. Then you can treat the rest of the possible keys as "none of the above" with CASE ELSE. In the following steps you'll copy a large piece of code from on-line help: QCARDS Code Entry 19 1. Move the cursor into the help window (press SHIFT+F6 twice). 2. Choose the Example hyperlink at the top of the screen to move the examples into the Help window (press E, then press F1). 3. Choose the Search menu's Find command (press ALT+S, then press F), type Example 2 in the text box, then press ENTER. 4. Scroll down (about 15 lines) to the line: IF LEN(Choice$) = 1 THEN 5. Select this line, and the next 43 lines, all the way down to END IF. (Be careful not to include the final LOOP statement in the selected text.) 6. Choose the Copy command from the Edit menu (press ALT+E, then press C). 7. Close the Help window (press ESC). This puts the cursor back on SELECT CASE in the View window. 8. Select the line SELECT CASE Choice$ (press SHIFT+END). 9. Choose the Paste command from the Edit menu (press ALT+E, then press P). The code pasted after the comment block should appear as follows: IF LEN(Choice$) = 1 THEN ' Handle ASCII keys SELECT CASE ASC(Choice$) CASE ESC PRINT "Escape key" END CASE IS 32, 127 PRINT "Control code" CASE 30 TO 29 PRINT "Digit: "; Choice$ CASE 65 TO 90 PRINT "Uppercase letter: "; Choice$ CASE 97 TO 122 PRINT "Lowercase letter: "; Choice$ CASE ELSE PRINT "Punctuation: "; Choice$ END SELECT ELSE ' Convert 2-byte extended code to 1-byte ASCII code and ' handle Choice$ = RIGHT$(Choice$, 1) SELECT CASE Choice$ CASE CHR$(DOWN) PRINT "DOWN arrow key" CASE CHR$(UP) PRINT "UP arrow key" CASE CHR$(PGDN) PRINT "PGDN key" CASE CHR$(PGUP) PRINT "PGUP key" CASE CHR$(HOME) PRINT "HOME key" CASE CHR$(ENDKEY) PRINT "END key" CASE CHR$(RIGHT) PRINT "RIGHT arrow key" CASE CHR$(LEFT) PRINT "LEFT arrow key" CASE ELSE BEEP END SELECT END IF Now test your work, then save it: QCARDS Code Entry 20 1. Choose the Run menu's Start command (press ALT+R, then press S). As you press keys, their names are printed on the QCARDS output screen. 2. Return to the QuickBASIC environment (press ESC). The ESC key case in the code you copied terminates the program. 3. Save the program as CHAPTER8.BAS. This example code works into QCARDS easily because handling keyboard input is a common task. You can copy, then adapt, this type of code for your programs. Editing the Block Copied from On-Line Help Examining and analyzing code from other programs is a great way to extend your programming skills. Modifying code from on-line help to work in your programs can also save you time. Each case in the SELECT CASE...END SELECT blocks deals with a key code representing a command the user can choose while using QCARDS. The following steps show you how to modify this block: QCARDS Code Entry 21 1. Select the whole first block (below the ' Handle ASCII keys comment, about line 225). It looks like this: SELECT CASE ASC(Choice$) CASE ESC PRINT "Escape key" END CASE IS < 32, 127 PRINT "Control code" CASE 30 TO 29 PRINT "Digit: "; Choice$ CASE 65 TO 90 PRINT "Uppercase letter: "; Choice$ CASE 97 TO 122 PRINT "Lowercase letter: "; Choice$ CASE ELSE PRINT "Punctuation "; Choice$ END SELECT This block displays the category of ASCII key the user presses. QCARDS already has a procedure named AsciiKey that examines the code of the key the user presses, then calls other procedures to carry out the user's commands. When you type in the call to AsciiKey (in the next step), what you type replaces this selected block. 2. Type the following line at the cursor: call AsciiKey(Choice$, TopCard, LastCard) The AsciiKey procedure is called with three arguments, which convey information AsciiKey needs to carry out its tasks. Choice$ contains the code for the key the user presses, TopCard contains the number of the card at the front of the screen, and LastCard holds the number representing the last record in the Index()array. 3. Indent the line you just entered two tab stops. The edited code should look like this (see Figure 8.3): File Edit View Search Run Debug Calls Options Hel ┌────────────────────────────── CHAPTER7.BAS ─────────────────────────┤ │' presses that represent numeric-keypad direction keys. │ │ IF LEN(Choice$) = 1 THEN │ ' Handle ASCII keys │ CALL AsciiKey(Choice$, TopCard, LastCard) │ ELSE │ ' Convert extended to ASCII and handle │ Choice$ = RIGHT$(Choice$, 1) │ ' │ SELECT CASE Choice$ │ CASE CHR$(DOWN) │ PRINT "DOWN arrow key" │ CASE CHR$(UP) │ PRINT "UP arrow key" │ CASE CHR$(PGDN) │ PRINT "PGDN key" │ CASE CHR$(PGUP) │ PRINT "PGUP key" │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> 00209: Figure 8.3 Code Showing Call to AsciiKey Procedure 4. Choose the Run menu's Start command (press ALT+R, then press S). Try issuing some of the QCARDS commands. You should be able to edit the card at the front of the screen. However, if you press the DIRECTION keys, you still just get a description of the key overprinted on the QCARDS screen. To begin to make QCARDS' DIRECTION keys functional, you'll need to edit more of the text you copied from on-line help, as follows: QCARDS Code Entry 22 1. Choose the QCARDS Quit command and return to QuickBASIC (press Q). 2. Place the cursor in the first column of the line PRINT "DOWN arrow key" 3. Select the whole line (press SHIFT+END), then replace it by typing this line: TopCard = TopCard - 1 This line is executed when the user presses the DOWN key. It decreases the value of the card representing the data at the front of the screen by one. This is the user's way of telling QCARDS to show the record whose number is one less than the current top card. 4. Indent the line, then edit the rest of the cases so the final block looks exactly as follows: SELECT CASE Choice$ CASE CHR$(DOWN) TopCard = TopCard - 1 CASE CHR$(UP) TopCard = TopCard + 1 CASE CHR$(PGDN) TopCard = TopCard - CARDSPERSCREEN CASE CHR$(PGUP) TopCard = TopCard + CARDSPERSCREEN CASE CHR$(HOME) TopCard = LastCard CASE CHR$(ENDKEY) TopCard = 1 CASE ELSE BEEP END SELECT The final two DIRECTION key cases (RIGHT and LEFT) of the block you copied from on-line help are not needed in QCARDS (since the cards cannot move sideways), so you can delete those cases. The CASE ELSE part of the statement is executed if the QCARDS user presses a key with an extended character code for which no other case is provided. 5. Save the program as CHAPTER8.BAS. You can replace the BEEP statement used in the CASE ELSE case of the Help example with a call to the Alarm procedure you created in Chapter 5, "The QCARDS Program." The following steps use the Find command to place an earlier call to the Alarm procedure on the Clipboard, then select this BEEP statement and replace it with CALL Alarm. Optional QCARDS Code Entry 4 1. Choose the Search menu's Find command (press ALT+S, then press F), type CALL Alarm in the text box, and press ENTER. 2. QuickBASIC searches for and then selects CALL Alarm, which was entered in the program in Chapter 5, "The QCARDS Program." 3. Choose the Edit menu's Cut command (press ALT+E, then press T). (The words CALL Alarm are selected, so you don't need to highlight them.) 4. Choose the Find command again, type BEEP in the text box, and press ENTER. The match is made with BEEP in the CASE ELSE statement. 5. Choose the Edit menu's Paste command to replace BEEP with CALL Alarm (press ALT+E, then press P). Finishing the QCARDS Code The SELECT CASE block changes the value of TopCard when the user presses DIRECTION keys, but doesn't do anything to actually change the information displayed on the cards. The following code lines take care of three eventualities that can arise from certain combinations of DIRECTION key presses, then shows the correct data on the cards: QCARDS Code Entry 23 1. Place the cursor on the line beneath the following comment (about line 252): ' Adjust the cards according to the key pressed by the user, ' then call the ShowCards procedure to show adjusted stack. 2. Create an empty line (press ENTER), then type the following code, exactly as shown: if TopCard < 1 then TopCard = LastCard + TopCard if TopCard > LastCard then TopCard = TopCard - LastCard if TopCard <= 0 then TopCard = 1 These three lines use the single line form of IF...THEN to "rotate" the card stack. They prevent TopCard from being passed to ShowCards when it has a value that is beyond the range of the Index()array. 3. Now type your final code line: CALL ShowCards(TopCard, LastCard) The ShowCards procedure places the proper data on the front card, and the proper name on each of the cards behind it. 4. Save the program now as CHAPTER8.BAS. 5. Choose the Run menu's Start command to run QCARDS (press ALT+R, then press S). Using QCARDS The commands on the command line at the bottom of the QCARDS output screen are now fully functional. Take a few minutes to try each feature. The commands are summarized in the following list: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ QCARDS Command Result ────────────────────────────────────────────────────────────────────────── Edit Top Lets you change any or all fields of the card at the front of the screen. Add New Places a "blank card" on the front of the screen for you to fill in. Copy to New Duplicates all fields of the current top card on a new card. QCARDS Command Result ────────────────────────────────────────────────────────────────────────── a new card. Delete Marks the current top card for deletion. Note that it is not actually deleted until you choose Quit. Therefore, if you decide not to delete the card, you can use CTRL+BREAK to break out of the program. When you restart, the card will still be there. Find Lets you move to one of the fields, then type what you want to search for. If an exact match is found, the card with the exact match is placed in the first position. If no exact match is found, QCARDS beeps. Sort Orders the cards alphabetically (or numerically) by the field in which you place the cursor. For example, if the cursor is in the zip code (Zip) field, Sort orders the cards in increasing zip QCARDS Command Result ────────────────────────────────────────────────────────────────────────── field, Sort orders the cards in increasing zip code order. If you place the cursor in the state (ST) field, the cards are ordered alphabetically by state. Print Prints out just the name and address fields (for use on a mailing label). Quit Writes the current Index array to the random-access disk file. If any cards have been marked as deleted, they are removed from the file at this time. Edits to cards and additions to the file are also made when you quit QCARDS. Quit then terminates the QCARDS program. ────────────────────────────────────────────────────────────────────────── Try the DIRECTION keys too. Most of the DIRECTION keys work. However, by copying code from Help, you inadvertently incorporated a naming inconsistency that caused a bug in your code. In the next chapter, you'll use QuickBASIC's debugging features to remove the bug. For More Information For more information on on-line help, see the following: Chapter Topic ────────────────────────────────────────────────────────────────────────── Section 10.8, "Using Information on QuickBASIC's Help menu commands On-Line Help" and and complete descriptions of all the Help Chapter 21, "The Help features. Menu" ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 9 Debugging While You Program Microsoft QuickBASIC's smart editor keeps your code free of syntax errors as you enter individual statements. But QuickBASIC has other features that help you isolate "bugs"──errors in the general logic or specific details of your program that cause it to behave in unanticipated ways. Some of these features are on the Debug menu, while others are on the Run menu. Still others are controlled completely by function keys. These features let you suspend program execution at any point, control which statements of your program execute, and monitor the values of variables. In this chapter, you'll find a real bug and fix it. You'll practice ■ Using QuickBASIC's debugging features ■ Defining and calling a procedure that has parameters ■ Creating a stand-alone executable file from within QuickBASIC This chapter takes about one to one and one-half hours to complete. Debugging Commands Most QuickBASIC debugging commands are on the Debug menu. However, some of the most useful debugging features are on the Run menu, or are accessible only through function keys. Debug-Menu Commands Commands on the Debug menu let you control program flow and monitor the value of variables in a running program. Command (and Shortcut Action Key) ────────────────────────────────────────────────────────────────────────── Add Watch Places a variable you specify into the Watch window, then continually updates its value. Instant Watch (SHIFT+F9) Gives current value of a highlighted variable; optionally, places the variable in Watch window. Delete Watch Deletes the specified variable from Watch window. Toggle Breakpoint (F9) Sets a "breakpoint" at the cursor if one is not currently set there. A breakpoint is a specified location where program execution will halt. If there is a breakpoint currently set at the cursor, choosing Toggle Breakpoint turns it off. Clear All Breakpoints Turns off all breakpoints everywhere in the program. ────────────────────────────────────────────────────────────────────────── Debugging Commands on the Run Menu Commands from the Run menu control program execution during debugging. Command (and Shortcut Action Key) ────────────────────────────────────────────────────────────────────────── Start (SHIFT+F5) Runs the program in the View window beginning with the first statement. Restart Resets all variables to zero (or zero-length strings), compiles declarations, and sets the first executable statement as the current statement. Continue (F5) Continues execution of a suspended program from the current statement. In a program that is not running, the effect is identical to the Start command. ────────────────────────────────────────────────────────────────────────── Function Keys Used in Debugging The following table shows the debugging commands that are controlled only by function keys: Command Action ────────────────────────────────────────────────────────────────────────── F7 Executes program to statement at the cursor. F8 Single steps through your program. Each time you press F8, the execution sequence progresses one statement. If the current statement is a procedure invocation, F8 moves the procedure definition into the View window. If the program is not already running, F8 acts the same as the Run menu's Restart command: pressing F8 restarts the program, making the first executable statement the current statement. In a suspended program, F8 executes the current statement in the execution sequence. F10 Single steps through your program. F10 steps over or executes all statements of a procedure as though they were a single statement without moving the procedure definition into the View window. Otherwise, F10 acts the same as F8. ────────────────────────────────────────────────────────────────────────── Debugging a Procedure In this section you'll use everything you've learned so far to turn the SELECT CASE block that handles DIRECTION keys into a procedure. In Chapter 5, "The QCARDS Program," you saw how easy it is to define procedures with QuickBASIC. The procedure you create in the next code-entry sequence is defined with parameters. When it is called, it is called with arguments. The following steps tell you how to create a SUB procedure with the name DirectionKey. As noted in Chapter 5, when QuickBASIC's smart editor processes the word sub followed by a procedure name, it opens a window and starts the procedure with the SUB and END SUB statements. QCARDS Code Entry 24 1. Start QuickBASIC if it is not already running, and open CHAPTER8.BAS. 2. Place the cursor in the leftmost column of the line containing SELECT CASE Choice$ (about line 231), then select the whole block (a total of 16 lines) down to and including END SELECT. It looks like this (see Figure 9.1): ┌────────────────────────────────────┐ │ │ │ Figure 9.1 can be found on │ │ page 132 of the printed manual. │ │ │ └────────────────────────────────────┘ Figure 9.1 Selecting the SELECT CASE Choice$ Block 3. Choose the Edit menu's Cut command to delete the text and place it on the Clipboard (press ALT+E, then press T). 4. Create a blank line above the END IF statement, then move the cursor to column 1 of the new blank line. 5. Type sub DirectionKey(Choice$, TopCard%, LastCard%) then press ENTER. Notice that QuickBASIC has started a SUB...END SUB procedure with the name you specified, and has moved it into the View window. 6. Put the cursor on the blank line immediately above the END SUB statement (press DOWN). 7. Choose the Edit menu's Paste command to paste the text block from the Clipboard. The procedure should look like Figure 9.2. File Edit View Search Run Debug Calls Options Help ┌──────────────────────── CHAPTER8.BAS:DirectionKey ──────────────────┤├── │DEFINT A-Z │SUB DirectionKey (Choice$, TopCard%, LastCard%) │ SELECT CASE Choice$ │ CASE CHR$(DOWN) │ TopCard = TopCard - 1 │ CASE CHR$(UP) │ TopCard = TopCard + 1 │ CASE CHR$(PGDN) │ TopCard = TopCard - CARDPERSCREEN │ CASE CHR$(PGUP) │ TopCard = TopCard + CARDPERSCREEN │ CASE CHR$(HOME) │ TopCard = LastCard │ CASE CHR$(ENDKEY) │ TopCard = 1 │ CASE ELSE │ CALL Alarm │ END SELECT │ │END SUB │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> 00003:013 Figure 9.2 DirectionKey Procedure in View Window Now that the procedure is defined, you have to put a CALL statement at the place where you deleted the text. The CALL statement makes the statements in a SUB procedure part of the program's execution sequence. Do the following: QCARDS Code Entry 25 1. Choose the View menu's SUBs command (press F2). Note that the fifth entry under CHAPTER8.BAS is now DirectionKey. 2. Select CHAPTER8.BAS if it isn't already selected. Press ENTER to return the cursor to the module-level code. 3. Move the cursor to the end of the following line (at about line 229): Choice$ = RIGHT$(Choice$, 1) 4. Create a blank line (press ENTER). Then, type the following line at the cursor but do not press ENTER: call DirectionKey(Choice$, TopCard, LastCard) The DirectionKey procedure is more complicated than Alarm because it is defined with parameters (the words in parentheses in the SUB statement you created earlier) and called with arguments (the words in parentheses in the CALL statement). You don't have to use the same names for the parameters as you use for the arguments, but it is all right to do so. The DirectionKey procedure makes QCARDS' module-level code easier to follow because the arithmetic for handling DIRECTION keys is now represented by a single statement, rather than 15 lines of statements. Using procedures costs almost nothing in terms of execution speed or program size, so the added program readability is worth the small effort of programming them. Procedures are especially beneficial for tasks that are performed repeatedly in a program. Learning about Procedures You can use QuickBASIC's debugging features to learn about procedures. The cursor should still be on the call you just typed to Direction Key (about line 226). Try the following: 1. Execute the program up to the call to DirectionKey (press F7). QCARDS starts to run. In the following step you will press a DIRECTION key while QCARDS is running, causing QuickBASIC to suspend execution at the call to DirectionKey. 2. Press a DIRECTION key (preferably PGUP). This returns control to the QuickBASIC environment. The statement CALL DirectionKey appears in high-intensity video. It hasn't been executed yet──it is the current statement. 3. Execute the CALL DirectionKey procedure as a single statement (press F10). The END IF statement appears in high-intensity video. It is now the current statement. Continuing a Suspended Program You don't always have to start suspended programs over from the beginning after making edits. Usually you can just choose the Continue command from the Run menu to continue execution from the point of suspension. QCARDS should run as before. When you press DIRECTION keys, the data on the cards should change. Try the following: 1. Continue program execution (press F5). 2. Press the END key on the numeric keypad to move the data on the cards to the last item. The END key doesn't work. If you did the optional code entry in Chapter 8, the Alarm procedure sounds off because the END key isn't recognized as one of the cases in the SELECT CASE block. (If you didn't do the optional code entry in Chapter 8, QCARDS beeps.) You have a bug. 3. Press the UP, DOWN, PGDN, and PGUP keys. They should all work. So there is a bug in the code dealing with the END key. 4. Return to QuickBASIC (press CTRL+BREAK). QuickBASIC returns you to the environment and places the cursor at either the Choice$ = INKEY$ statement, or LOOP WHILE Choice$ = statement, whichever was executing when you pressed CTRL+BREAK. Right now you are stuck in this DO loop. You cannot step past it with F8 or F10. You will have to place the cursor on the statement following the loop, then use F7 to execute to it. 5. Move the cursor down (about 27 lines) past the big comment block to the following line (at about line 224): IF LEN(Choice$) = 1 THEN 6. Execute the program to the statement at the cursor (press F7). The QCARDS screen is displayed. 7. Press the END key again. QuickBASIC returns you to the environment. The line you were on when you pressed F7 is highlighted: IF LEN(Choice$) = 1 THEN Usually when you suspend program execution you can press F5 to continue execution from the point of suspension. However, some edits you make to a suspended program prevent simple continuation. In the next few QCARDS code-entry sequences, QuickBASIC may display a dialog box indicating that one of the edits you have made requires restarting the program (see Figure 9.3). That is normal. Just press ENTER and continue editing. ┌────────────────────────────────────────────────────────────────────────── │ │ You will have to restart your program after this edit. Proceed anyway? │ ├────────────────────────────────────────────────────────────────────────── │ < OK > < Cancel > < Help > └────────────────────────────────────────────────────────────────────────── Figure 9.3 Restart Program Error Message Isolating a Bug QuickBASIC's debugging features make coding and logic errors easy to trace and fix because they make it easy to understand the line-by-line workings of your code. In the next QCARDS code-entry sequence, you'll use single stepping to find the bug. You know you pressed a DIRECTION key to suspend the program so you can anticipate that execution will move to the ELSE block when you execute the statement at the cursor. Follow these steps to track down the bug: QCARDS Code Entry 26 1. Execute the IF statement and the one that follows and move the cursor to the call to DirectionKey (press F8 twice to single step up to the call). 2. Single step into the DirectionKey procedure (press F8). The cursor is placed on the SELECT CASE statement. 3. Set a breakpoint (see Figure 9.4) at the current line (press F9). Breakpoint │ File Edit View Search Run Debug Calls Options │ Hel ┌─────────────────────── CHAPTER8.BAS:DirectionKey ──────┼────────────┤ │DEFINT A-Z │ │SUB DirectionKey (Choice$, TopCard%, LastCard%) │ │ SELECT CASE Choice$ │ CASE CHR$(DOWN) │ TopCard = TopCard - 1 │ CASE CHR$(UP) │ TopCard = TopCard + 1 │ CASE CHR$(PGDN) │ TopCard = TopCard - CARDPERSCREEN │ CASE CHR$(PGUP) │ TopCard = TopCard + CARDPERSCREEN │ CASE CHR$(HOME) │ TopCard = LastCard │ CASE CHR$(ENDKEY) │ TopCard = 1 │ CASE ELSE │ CALL Alarm │ END SELECT │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ <Shift+F1=Help> <F5=Continue> <F9=Toggle Bkpt> <F8=Step> 00017: Figure 9.4 Setting a Breakpoint 4. Continue execution of QCARDS (press F5 twice). When the QCARDS output screen appears, press the END key to activate the suspected bug. QuickBASIC returns the cursor to the line on which you set the breakpoint. 5. Single step to the CASE ELSE statement (press F8). The CALL Alarm statement appears in reverse video. 6. Move the cursor into the word HOME in the CASE CHR$(HOME) statement, then get help (press F1). The Help window opens and describes HOME as a symbolic constant with a value of 71 (see Figure 9.5). File Edit View Search Run Debug Calls Options Hel ┌─────────────────────────────── HELP: HOME ──────────────────────────┤ │HOME is a symbol that is used in your program as follows: │ │┌ C:\QB4.5\DEMO\DIR1\CHAPTER8.BAS ──── ││ constant of type: INTEGER Value = 71 ││ │ │ ├─────────────────────── CHAPTER8.BAS:DirectionKey ───────────────────┤ │ TopCard = TopCard - CARDPERSCREEN │ CASE CHR$(PGUP) │ TopCard = TopCard + CARDPERSCREEN │ CASE CHR$(HOME) │ TopCard = LastCard │ CASE CHR$(ENDKEY) │ TopCard = 1 │ CASE ELSE │ CALL Alarm │ END SELECT │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ───────────────────────────── │ │ <Shift+F1=Help> <F5=Continue> <F9=Toggle Bkpt> <F8=Step> 00012: Figure 9.5 Symbol Help for Symbolic Constant HOME 7. Move the cursor down to the CASE CHR$(ENDKEY) statement, place the cursor in the word ENDKEY, and get help (press F1). The Help window opens and describes ENDKEY as a variable of type INTEGER. But ENDKEY should be a symbolic constant, just like HOME. 8. Choose the Instant Watch command from the Debug menu. The value of ENDKEY is shown as zero. 9. Press ENTER to place ENDKEY in the Watch window. In the program, ENDKEY should be a symbolic constant defined with a CONST statement in the declarations and definitions section of the program (just like HOME). Try this: QCARDS Code Entry 27 1. Choose the View menu's SUBs command (press ALT+V, then press S), then choose the first entry (CHAPTER8.BAS) in the list box to move the module-level code of the program into the View window. 2. Move the cursor to the top of the module-level code (press CTRL+HOME). 3. Choose the Search menu's Find command, then type HOME in the text box and press ENTER. HOME is selected in the declarations and definitions section. Beside it, you can see the cause of the bug. The symbolic constant used to represent the END key is ENDK, whereas the SELECT CASE code you copied from on-line help used ENDKEY to represent the END key (see Figure 9.6). File Edit View Search Run Debug Calls Options Help DirectionKey ENDKEY: 0 ┌────────────────────────────── HELP: ENDKEY ─────────────────────────┤├── │ENDKEY is a symbol that is used in your program as follows: │ │┌ C:\QB4.5\DEMO\DIR1\CHAPTER8.BAS ──── ││┌ SUB DirectionKey ─────────────────── │││ variable of type: INTEGER ││ ├────────────────────────────── CHAPTER8.BAS ─────────────────────────┤├── │CONST SPACE = 32, ESC = 27, ENTER = 13, TABKEY = 9 │CONST DOWN = 80, UP = 72, LEFT = 75, RIGHT = 77 │CONST HOME = 71, ENDK = 79, PGDN = 81, PGUP = 73 │CONST INS = 82, DEL = 83, NULL = 0 │CONST CTRLD = 4, CTRLG = 7, CTRLH = 8, CTRLS = 19, CTRLV = 22 │ │' Define English names for color-specification numbers. Add BRIGHT to │' any color to get bright version. │CONST BLACK = 0, BLUE = 1, GREEN = 2, CYAN = 3, RED = 4, MAGENTA = 5 │CONST YELLOW = 6, WHITE = 7, BRIGHT = 8 │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── │ │ <Shift+F1=Help> <F5=Continue> <F9=Toggle Bkpt> <F8=Step> 00024:007 Figure 9.6 Error in Naming Symbolic Constant for the ENV Key Most of the symbolic-constant names used to represent the DIRECTION keys are the same as those shown on the keys themselves, but you can't represent the END key with the symbolic constant END, because END is a BASIC keyword. The on-line help example used ENDKEY to deal with this problem, QCARDS uses ENDK. It doesn't matter which is used, ENDKEY is just as good as ENDK. What is important is that the word used in the definition be the same as that used elsewhere in the program. Do the following to change ENDKEY to ENDK: QCARDS Code Entry 28 1. Choose the Search menu's Change command (press ALT+S, then press C). (If you get a message saying you will have to restart your program, press ENTER.) 2. Type ENDKEY in the first text box, then press TAB and type ENDK in the second text box. 3. Start the search (press ENTER). The first match is in the DirectionKey procedure. 4. Make the change (press C). The search ends. That was the only occurrence of ENDKEY. Closing the Watch Window When the Watch window is open, QuickBASIC executes more slowly than when it is closed. You close the Watch window by repeatedly choosing the Delete Watch command from the Debug menu, then choosing variables from the resulting dialog box until the Watch window closes. You may also want to occasionally choose the Clear All Breakpoints command too. 1. Choose the Debug menu's Clear All Breakpoints command (press ALT+D, then press C). 2. Choose the Debug menu's Delete Watch command (press ALT+D, then press D). 3. Delete the entry (press ENTER). The next step is to run your program and save it. Do the following: QCARDS Code Entry 29 1. Choose the Run menu's Start command. QCARDS should run and recognize all the DIRECTION keys as well as all the command-line keys. 2. Choose Quit from the QCARDS command line, then press a key to continue. 3. Choose the File menu's Save As command and save the program as FINALQ.BAS. QCARDS should now be fully functional. Automatic Procedure Declarations When you save a program, QuickBASIC creates a DECLARE statement for any new procedure. Generally, you should move such DECLARE statements to the declarations and definitions section of your program. QuickBASIC uses procedure declarations to check the number, order, and types of the arguments you pass to a procedure when you call it. DECLARE statements should be toward the end of the declarations and definitions below statements such as DEFtype and TYPE...END TYPE. You should copy the DECLARE statement for the procedure DirectionKey into the procedure-declarations portion of the declarations and definitions (as you did with the declaration for Alarm in Chapter 5). Do the following: QCARDS Code Entry 30 1. Move to the beginning of the program (press CTRL+HOME). 2. Select the entire DECLARE DirectionKey statement (press SHIFT+END). 3. Delete the selected statement from QCARDS and place it on the Clipboard (press ALT+E, then press T). 4. Move to the SUB procedure declarations section of the program (about line 74). 5. Create a blank line (if necessary) and insert the DECLARE DirectionKey statement (press ALT+E,then press P). 6. Save the program again as FINALQ.BAS. Creating a Stand-Alone Executable File 1. Choose the Run menu's Make EXE File command (press ALT+R, then press X). If a dialog box appears asking if you want to save your files, press ENTER. The Make EXE File dialog box appears (see Figure 9.7): Type name of executable file here. │ ┌───────────────────┼──Make EXE File─────────────────────────────┐ │ ┌───┼───────────────────────────────────────┐ │ │EXE File Name: │FINALQ.EXE │ │ │ └───────────────────────────────────────────┘ │ │ Produce: │ │ [ ] Produce Debug Code ( ) EXE Requiring BRUN45.EXE │ │ (∙) Stand-Alone EXE File │ ├────────────────────────────────────────────────────────────────┤ │ < Make EXE > < Make EXE and Exit > < Cancel > < Help > │ └────────────────────────────────────────────────────────────────┘ Figure 9.7 Make EXE File Dialog Box 2. Type QCARDS in the text box. 3. Choose the Make EXE and Exit option (press ALT+E). QuickBASIC creates the EXE file and exits to DOS. 4. Run QCARDS (type qcards at the DOS prompt and press ENTER). ────────────────────────────────────────────────────────────────────────── NOTE If you don't have a hard disk, QuickBASIC prompts you to insert a disk containing BC.EXE, and later prompts you for a path for libraries it needs to finish making the executable file. BC.EXE, LINK.EXE and BRUN45.LIB are on disk 3 (Utilities 1). BCOM45.LIB is located on disk 4 (Utilities 2). When asked for a path, type in a full path including both drive name and file name. ────────────────────────────────────────────────────────────────────────── Learning about QuickBASIC's Other Menu Items The preceding chapters have familiarized you with most of the commands on QuickBASIC's Easy Menus. Two commands were not covered. The Options menu's Set Paths command lets you change some settings that were made automatically by the Setup program you used to install QuickBASIC. The View menu's Included Lines command is used only in programs that rely on include files. See Sections 20.2, "Set Paths Command," and 14.7, "Included Lines Command," for full discussions of these commands. Easy Menus provides a very functional programming environment for the novice or intermediate BASIC user. QuickBASIC's Full Menus provide additional commands needed for advanced or professional programming. For example, the Full Menus Debug menu contains commands useful for debugging large and complex programs. The Full Menus File menu lets you load multiple files simultaneously, so you can create programs using multiple, separately compiled source files (modules). The uses of these advanced commands are covered in Chapters 10-21 of this manual. The programming techniques are discussed in Programming in BASIC. For More Information For more information on the topics discussed in these chapters, see the following: Chapter Topic ────────────────────────────────────────────────────────────────────────── Chapter 2, "SUB and Complete information on programming with FUNCTION Procedures," procedures, including rules for parameters and in Programming in BASIC arguments. Chapter 17, "Debugging Complete rules for using all QuickBASIC's Concepts and debugging features, including advanced features Procedures," Chapter such as watchpoints and the Calls menu. 18, "The Debug Menu," and Chapter 19, "The Calls Menu" ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── PART 3 QUICKBASIC MENUS AND COMMANDS ──────────────────────────────────────────────────────────────────────────── Part 3, "QuickBASIC Menus and Commands," is a reference to the Microsoft QuickBASIC menus and commands. Refer to this part when you want detailed information on how a command works or situations in which you might use the command. Chapters 10 and 11 introduce the QuickBASIC environment and working with your files. Chapters 12-16 look at the QuickBASIC features that help you create, edit, and run your programs. Chapters 17-19 cover general debugging techniques and the specific tools available for faster debugging. Chapter 20 discusses how you can customize QuickBASIC to your personal taste, and Chapter 21 reviews the menu commands for accessing the on-line help system. ──────────────────────────────────────────────────────────────────────────── Chapter 10 Getting Around in QuickBASIC This chapter introduces the QuickBASIC programming environment and illustrates many of its features. The chapter includes the basic information you'll need to begin using the QuickBASIC program development environment. This chapter tells you how to do the following: ■ Start QuickBASIC ■ Choose commands from menus ■ Choose items in dialog boxes ■ Scroll listings ■ Select text in a dialog box or window ■ Change window size ■ Use the Immediate window ■ Use the Watch window ■ Use the mouse ■ Use on-line help 10.1 Starting QuickBASIC This section discusses starting QuickBASIC with and without special options. It also describes the parts of the QuickBASIC screen. If you have not already done so, read Chapter 1, "Setting Up QuickBASIC," to set up QuickBASIC on your computer. 10.1.1 The QB Command To start QuickBASIC, type QB at the DOS prompt. The full syntax for the QB command is the following: QB [[[[/RUN]] [[programname]] [[/B]] [[/G]] [[/H]] [[/NOHI]] [[/C:buffersize]] [[/L[[libraryname]]]] [[MBF]] [[/AH]] [[/CMD string]]]] ────────────────────────────────────────────────────────────────────────── NOTE In this manual, the QB command and its options appear in uppercase letters. However, because DOS is not case sensitive, you may use lowercase letters as well. ────────────────────────────────────────────────────────────────────────── The following list describes QuickBASIC's command options. These options can be typed on the DOS command line following the QB command and have the effects described. Use the options in the order listed. ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Option Description ────────────────────────────────────────────────────────────────────────── /RUN programname Causes QuickBASIC to load and run programname before displaying it. programname Names the file to be loaded when QuickBASIC starts. /B Allows the use of a composite (black-and-white) monitor with a color graphics card. The /B option displays QuickBASIC in black and white if you have a color monitor. /G Sets QuickBASIC to update a CGA screen as fast as possible. The option works only with machines using CGA monitors. If you see "snow" (dots flickering on the screen) when QuickBASIC updates your screen, then your hardware cannot fully support the /G option. If you prefer a "clean" screen, restart QuickBASIC without the option. Option Description ────────────────────────────────────────────────────────────────────────── screen, restart QuickBASIC without the option. /H Displays the highest resolution possible on your hardware. /NOHI Allows the use of a monitor that does not support high intensity. See Section 10.1.2 for a description of this option. /C:buffersize Sets the size of the buffer receiving data. This option works only with an asynchronous communications card. The default buffer size is 512 bytes; the maximum size is 32,767 bytes. /L libraryname Loads the Quick library that is specified by libraryname. If libraryname is not specified, the default Quick library, QB.QLB, is loaded. /MBF Causes the QuickBASIC conversion functions to Option Description ────────────────────────────────────────────────────────────────────────── /MBF Causes the QuickBASIC conversion functions to treat IEEE-format numbers as Microsoft Binary format numbers. /AH Allows dynamic arrays of records, fixed-length strings, and numeric data to be larger than 64K each. /CMD string Passes string to the COMMAND$ function. This option must be the last option on the line. ────────────────────────────────────────────────────────────────────────── For example, type QB /RUN GRAPHIX /G /AH if you want to run a program named GRAPHIX with the following options: ■ Load and run Graphix before displaying it ■ Quickly update CGA screen ■ Allow dynamic arrays to exceed 64K Generally, however, you start QuickBASIC by typing QB and pressing ENTER. 10.1.2 The /NOHI Option If you type QB at the DOS level, QuickBASIC assumes you have a monitor that can display high intensity. However, if you use a monitor that does not support high intensity, you will need to tell QuickBASIC how to display on your system. Use the list below to determine any options you may need. Monitor Display Invocation Command ────────────────────────────────────────────────────────────────────────── 16 colors (CGA, EGA or VGA) QB 4-color monochrome (MDA) QB 8 colors (CGA, EGA or VGA) QB /NOHI 4-color black-and-white composite (CGA, EGA or VGA) QB /B 2-color black-and-white composite (CGA, EGA or VGA) QB /B /NOHI ────────────────────────────────────────────────────────────────────────── Laptop computers frequently use liquid crystal displays (LCDs) that are considered 2-color black-and-white composite displays; they require the QB /B /NOHI command. 10.1.3 The QuickBASIC Screen The first time you type QB and press ENTER from DOS, a dialog box offers you the opportunity to review the QuickBASIC Survival Guide. If you press ESC to clear the dialog box, you now see the QuickBASIC screen, shown in Figures 10.1 and 10.2. Figure 10.1 shows the top half of the QuickBASIC invocation screen. ┌────────────────────────────────────┐ │ │ │ Figure 10.1 can be found on │ │ page 153 of the printed manual. │ │ │ └────────────────────────────────────┘ Figure 10.1 Top Half of QuickBASIC Invocation Screen The following list describes the items shown in Figure 10.1. ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Item Description ────────────────────────────────────────────────────────────────────────── Menu bar Names each menu. When you press the ALT key, the highlighted letter indicates which key "pulls down" that menu. View window Displays your program's text. Cursor Shows where the text you type will appear. The cursor appears in the active window. Mouse cursor Shows current on-screen position of mouse (use with mouse only). Item Description ────────────────────────────────────────────────────────────────────────── with mouse only). Title bar Shows the name of the program or procedure. Maximize box Expands the active window to fill the screen (use with mouse only). Scroll arrow Scrolls the text one character or one line at a time (use with mouse only). Scroll box Shows cursor's relative position within the file or procedure. ────────────────────────────────────────────────────────────────────────── Figure 10.2 shows the bottom half of the QuickBASIC invocation screen. ┌────────────────────────────────────┐ │ │ │ Figure 10.2 can be found on │ │ page 154 of the printed manual. │ │ │ └────────────────────────────────────┘ Figure 10.2 Bottom Half of QuickBASIC Invocation Screen ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Item Description ────────────────────────────────────────────────────────────────────────── Immediate window Executes QuickBASIC statements directly; they need not be entered as part of a program. CAPS LOCK and NUM LOCK C appears when the CAPS LOCK key is toggled on. N indicators appears when the NUM LOCK key is toggled on. Scroll bars Scrolls text in the currently active window (use with mouse only). Reference bar Contains reference information. Item Description ────────────────────────────────────────────────────────────────────────── Reference bar Contains reference information. The first five items are buttons showing a frequently used shortcut key and the corresponding menu or option. Clicking a button with the mouse gives the same result as pressing the shortcut key shown in the button. Pressing ALT displays four different reference items. WordStar-style command 'Q appears when you enter CTRL+Q, a indicator WordStar-style command. 'K appears here when you are setting a place marker (see Section 12.4, "Using Placemarkers in Text"). 'P appears here when you are entering a literal character (see Section 12.6, "Entering Special Characters"). Line and column counters Give current position of cursor within the text in the active window. ────────────────────────────────────────────────────────────────────────── Item Description ────────────────────────────────────────────────────────────────────────── When you start QuickBASIC without specifying a program name, you can begin to write a program, or you can ask for on-line help. To use the QuickBASIC on-line help, press F1 for a general Help window, or use the Help menu for more detailed information (see Section 10.8, "Using On-Line Help," and Chapter 21, "The Help Menu," for more details). To clear a Help window, press the ESC key. Pressing ESC also clears menus, dialog boxes, and error messages from the QuickBASIC screen. 10.2 Opening Menus and Choosing Commands QuickBASIC commands are organized in pull-down menus on the menu bar. Figure 10.3 shows one of these, the File menu. ┌──────┐ │ File │ ├──────┴──────────┐ │ New Program │ │ Open Program... │ │ Merge... │ │ Save │ │ Save As... │ │ Save All │ ├─────────────────┤ │ Create File... │ │ Load File... │ │ Unload File... │ ├─────────────────┤ │ Print... │ │ DOS Shell │ ├─────────────────┤ │ Exit │ └─────────────────┘ Figure 10.3 The File Menu The QuickBASIC environment is designed for fast, simple operation. You can do most operations in QuickBASIC with either of the following techniques: ■ Open menus and choose commands with the keyboard or a mouse. (See Section 10.7, "Using the Mouse," for a summary of mouse techniques.) ■ Execute a command directly with a "shortcut" key, which is one or two keystrokes that perform the same task as a menu command. Menu commands followed by three dots (...) indicate that more information is required before the command can execute. In these cases, a "dialog box"──a box that asks you for additional information──appears on the screen. 10.2.1 Keyboard Technique You can choose any command on a QuickBASIC menu by using the keyboard. To open a menu, follow these steps: 1. Press and release the ALT key. (Notice that after you press the ALT key, the first letter of each menu is highlighted.) 2. Press the first letter of the menu's name. ────────────────────────────────────────────────────────────────────────── NOTE The ALT key is a "toggle," so if you press it again, the highlight disappears. The "press and release" feature of the ALT key is active only within menus. When using key combinations in other circumstances, you must hold down the first key while pressing the rest of the sequence. ────────────────────────────────────────────────────────────────────────── This "selects" (highlights) the entire menu and displays the menu's commands. A command name contains a highlighted letter whenever it is "active" (available). If no letter in a command is highlighted and it appears dimmed, you cannot choose that command until you take some other action. For example, if you are editing a program but have not selected any text to copy or delete, the commands Cut and Copy can have no effect. You can use Cut and Copy only after you select text. (See Section 12.2 to learn how to select text for copying or deleting.) To move from one menu to another, do either of the following: ■ Close the menu by pressing ESC, then repeat steps 1 and 2 above. ■ Press the LEFT or RIGHT direction keys. To choose a command, do one of the following: ■ Press the key corresponding to the highlighted letter. ■ Use the UP or DOWN direction keys to highlight the command you want to execute, then press ENTER. Some commands take effect immediately and cannot be canceled once chosen. However, commands followed by three dots ( ... ) cause QuickBASIC to display a dialog box so you can supply additional information. To cancel a dialog box, press ESC. See Section 10.3 for a discussion of dialog boxes. See Also Section 10.7, "Using the Mouse" 10.2.2 Using Shortcut Keys In QuickBASIC the function keys (F1-F10) serve as shortcut keys for many of the menu functions. Shortcut keys allow you to substitute one or two keystrokes for the process of choosing a command through on-screen menus. Shortcut keys for menu commands are listed on the menu, next to the command. If you are new to programming you may prefer to use only the on-screen menus. When you feel comfortable with QuickBASIC commands, you may want to use the shortcut keys. For example, to run a program, you can choose the Start command from the Run menu, or you can bypass the menu and use the shortcut-key combination SHIFT+F5. Table 10.1 lists and explains all of the QuickBASIC shortcut keys and equivalent menu commands. Table 10.1 QuickBASIC Shortcut Keys ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Programming Action Shortcut Keys Menu Command ────────────────────────────────────────────────────────────────────────── SHIFT+F1 Displays general help information Help on Help command on Help menu F1 Displays help information on the keyword or variable nearest to the left of the cursor Topic command on Help menu ALT+F1 Displays up to 20 previous help screens None F2 Displays a list of loaded SUB or FUNCTION procedures, modules, include files, or document files SUBs command on View menu SHIFT+F2 Displays next procedure in active window Next SUB command on View menu Programming Action Shortcut Keys Menu Command ────────────────────────────────────────────────────────────────────────── CTRL+F2 Displays previous procedure in active window None F3 Finds next occurrence of previously specified text Repeat Last Find command on Search menu F4 Toggles display of output screen Output Screen command on View menu F5 Continues program execution from current statement Continue command on Run menu SHIFT+F5 Starts program execution from beginning Start command on Run menu Programming Action Shortcut Keys Menu Command ────────────────────────────────────────────────────────────────────────── F6 Makes next window the active window None SHIFT+F6 Makes previous window the active window None F7 Executes program to current cursor position None F8 Executes next program statement, traces through procedure None SHIFT+F8 Steps back in your program through the last 20 program statements recorded by the History On or Trace On command None Programming Action Shortcut Keys Menu Command ────────────────────────────────────────────────────────────────────────── None F9 Toggles breakpoint Toggle Breakpoint command on Debug menu SHIFT+F9 Displays Instant Watch dialog box Instant Watch command on Debug menu F10 Executes next program statement, traces around procedure None SHIFT+F10 Steps forward in your program through the last 20 program statements recorded by the History On or Trace On command None CTRL+F10 Toggles between multiple windows and full screen Programming Action Shortcut Keys Menu Command ────────────────────────────────────────────────────────────────────────── CTRL+F10 Toggles between multiple windows and full screen for active window None ────────────────────────────────────────────────────────────────────────── See Also Section 12.7, "Summary of Editing Commands" 10.3 Using Dialog Boxes QuickBASIC displays a dialog box when it needs additional information before it can carry out an action. For example, a dialog box might do the following: ■ Prompt you for the name of a file ■ Display a list of options ■ Ask you to verify or cancel a command ■ Alert you to an error Figures 10.4 and 10.5 illustrate the parts of a dialog box. Path-specification Text box List boxes line │ ││ ┌┼────────────────────┼─────── Load File ─────────────┼┼─────────────────── ││ ┌────────┼───────────────────────────────┼┼─────────────────┐ ││File Name: │*.bas ││ │ ││ └────────────────────────────────────────┼┼─────────────────┘ │└C:\QB4.5\DEMO ││ │ Files ││ Dirs/Drives │ ┌──────────────────────────────────────────────────┐││ ┌───────────────┐ │ │ ATEST.BAS SORTDEMO.BAS │││ │ .. │ │ BL.BAS TEST.BAS ─┼┘└─┼ SOURCE ▒ │ │ DEMO1.BAS TORUS.BAS │ │ [-A-] ▒ │ │ DEMO2.BAS VARHELP.BAS │ │ [-B-] ▒ │ │ DEMO3.BAS VARHELP2.BAS │ │ [-C-] ▒ │ │ QBFORMAT.BAS │ │ ▒ │ │ QCARDS.BAS │ │ ▒ │ │ REMLINE.BAS │ │ │ └▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒┘ └───────────────┘ │ ┌────────────┬───────────┬────────────┐ │ │ Load as: (∙) Module ( ) Include ( ) Document ├─┼──────────────────────────────────────────────────────────────────────── │ │ < OK > < Cancel > < Help > └─┼───────────┼─────────────────┼───────────────────┼────────────────────── │ └──────────┬──────┴───────────────────┘ Option buttons Command buttons Figure 10.4 Load File Dialog Box Option buttons │ ┌┼─────────────────────────────── Display ───────────────────────────────── ││ ┌────────────────────────────── Colors ──────────────────────────────┐ ││ │ Foreground Background │ ││ │ ┌─────────┐ ┌─────────┐ │ ││ │ ┌(∙) 1. Normal Text │ Black │ Black │ ││ │ │ │ White ▒ │ White ▒ │ │└─┼─┤( ) 2. Current Statement │ Gray ▒ │ Gray ▒ │ │ │ │ │ BrWhite ▒ │ BrWhite ▒ │ │ │ └( ) 3. Breakpoint Lines │ ▒ │ ▒ │ │ │ │ ▒ │ ▒ │ │ │ │ ▒ │ ▒ │ │ │ │ │ │ │ │ └─────────┘ └─────────┘ │ │ │ │ │ └────────────────────────────────────────────────────────────────────┘ │ │ ┌───────────────────────── Display Options ──────────────────────────┐ │ │ [X] Scroll Bars Tab Stops: 8 │ │ └─────┼──────────────────────────────────────────────────────────────┘ ├────────┼───────────────────────────────────────────────────────────────── │ │ < OK > < Cancel > < Help > └────────┼───────────────────────────────────────────────────────────────── Check box Figure 10.5 Display Dialog Box To move between different parts of a dialog box, use one of the following methods: ■ Press the TAB key. ■ Hold down the ALT key while pressing the key corresponding to the highlighted letter in the item you want selected. When a dialog box opens, it usually contains any options set previously. The different dialog box components are described in the following list: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Component Description ────────────────────────────────────────────────────────────────────────── Path-specification line Displays the path to the current directory. Change the path by either typing a new path name in the text box or by selecting the appropriate Component Description ────────────────────────────────────────────────────────────────────────── in the text box or by selecting the appropriate directory in the Dirs/Drives list box. Text box Displays typed text. List box Lists a group of similar items, such as files or procedures available, from which you may choose one. Use the DIRECTION keys to move within list boxes. Check box Toggles an option on or off. Once the cursor is in the checkbox area, press SPACEBAR, or press ALT and then the highlighted letter of the item you want to turn on or off. When an option is on, an X appears in the check box; when it is off, the check box is empty. Option button Selects one of a group of options. Only one of Component Description ────────────────────────────────────────────────────────────────────────── Option button Selects one of a group of options. Only one of the group may be chosen at a time. Use the DIRECTION keys to move among option buttons. Command button Executes a command. Once the cursor is in the command button area, use TAB to alter selections. Press either SPACEBAR or ENTER to execute commands. ────────────────────────────────────────────────────────────────────────── Note that within dialog boxes you must keep the ALT key pressed while pressing the high-intensity letter. This procedure is slightly different from the one for choosing menu commands, which does not require you to hold the ALT key down while pressing the highlighted letter. 10.4 Using Windows Microsoft QuickBASIC uses windows to contain different types of information. There are four window types──View, Immediate, Help, and Watch. This section introduces QuickBASIC's windows and tells how to do the following: ■ Change the active window ■ Move different parts of programs in and out of an active window ■ Change the size of a window ■ Scroll text in a window 10.4.1 Window Types QuickBASIC uses different windows to perform different functions. The following list describes the types of windows in QuickBASIC: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Window Description ────────────────────────────────────────────────────────────────────────── View The window that appears at the top of the screen Window Description ────────────────────────────────────────────────────────────────────────── View The window that appears at the top of the screen when you start QuickBASIC (see Figure 10.1). When you load a program, the code that is outside of any FUNCTION or SUB procedure──known as the "module-level" code──appears in the View window. The View menu contains commands that let you easily move different parts of your program in and out of View windows. For example, to see a FUNCTION or SUB procedure in the View window, choose the SUBs command from the View menu, then select the procedure from the dialog box. Immediate The window at the bottom of the screen when you start QuickBASIC. The Immediate window allows you to execute BASIC statements immediately. (See Section 17.3.5 for more information on the Immediate window.) Help The window that contains on-line help. You can Window Description ────────────────────────────────────────────────────────────────────────── Help The window that contains on-line help. You can copy examples from Help windows and paste them into your program. Watch The window that opens at the top of the screen when you choose certain commands from the Debug menu. It displays the values of variables as your program runs. (See Section 17.3.4 for more information on using the Watch window for debugging.) ────────────────────────────────────────────────────────────────────────── 10.4.2 Splitting the View Window (Full Menus Only) You can split the View window into upper and lower windows; this allows you to view or edit two parts of a program simultaneously. Because the View window can be split in two (Full Menus only), you can have a total of five windows open at one time (two View windows, the Immediate window, the Help window, and the Watch window), as shown in Figure10.6. Help window Watch window View windows │ │ ││ │ File Edit View Search│ Run Debug Calls Options ││ Help │DEMO2.BAS NUM: │ ││ │DEMO2.BAS TOTAL: ││ ┌┼───────────────── HELP: DECLARE Statement QuickSCREEN ──────────┼┼──┤├── │└ QuickSCREEN Details Example Contents Index │─────────────────────────────────────────────────────────────────┼┼────── │DECLARE - a non-executable statement that declares references to ││ │ BASIC procedures and invokes argument type checking ││ │Syntax ││ │ DECLARE {FUNCTION | SUB } name [<[parameterlist]>] ││ ├─────────────────────────────── DEMO2.BAS ───────────────────────┼┼──┤├── │DECLARE SUB Bounce (Hi%, Low%) │└ │DECLARE SUB Fall (Hi%, Low%, Del%) │ │DECLARE SUB Siren (Hi%, Rng%) │ │DECLARE SUB Klaxon (Hi%, Low%) │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒ ├────────────────────────────── SORTDEMO.BAS ─────────────────────┼───┤├── │' The program also uses SOUND statements to generate different pitches, │' depending on the location of the bar being printed. Note that the SOUND │' statements delay the speed of each sorting algorithm so you can follow │' the progress of the sort. Therefore, the times shown are for comparison ├─────────────────────────────── Immediate ──────────────────────────────── │LOCATE 4,5 : PRINT "TEST" │ │ <Shift+F1=Help>│<F6=Window> <F2=Subs> <F5=Run> <F8=Step> 00001:001 │ Immediate window Figure 10.6 QuickBASIC Screen with Five Windows Open To split the View window, choose the Split command from the View menu. The screen is now divided into two parts. Repeat the process to restore the original screen. See Also Section 14.3 "Split Command" 10.4.3 Changing the Active Window The window that contains the cursor is referred to as the "active" window; it is the place where text entered from the keyboard appears. To make another window active, follow these steps: ■ Press F6 to cycle downward through the windows on the screen. ■ Press SHIFT+F6 to cycle upward. 10.4.4 Changing Window Size You can increase or decrease the size of a window one line at a time or expand it to fill the whole screen. To change the size of a window, first make it the active window. Then use the following key combinations (hold down the first key while pressing the second) to increase or decrease the window's size. (Use the PLUS and MINUS keys on the keypad.) Key Combination Result ────────────────────────────────────────────────────────────────────────── ALT+PLUS (+) Expands the active window one line. ALT+MINUS (-) Shrinks the active window one line. CTRL+F10 Expands the active window to fill the screen, or, if it already occupies the whole screen, returns the active window to its former size. If the View window is split in two when you press CTRL+F10, pressing CTRL+F10 again restores both windows to the screen. ────────────────────────────────────────────────────────────────────────── 10.4.5 Scrolling in the Active Window To look at the parts of a file that do not fit within the boundaries of a View window, you can move the text ("scroll") up, down, right, or left. Once you reach a window's edge, press the appropriate DIRECTION key to begin scrolling. For example, to scroll right one character at a time, go to the rightmost character on the screen and press the RIGHT key. Refer to Table 10.2 for information on scrolling more than one character at a time. The rightmost column in this table shows keystrokes that you may find more convenient if you prefer WordStar-style commands. Table 10.2 Scrolling WordStar-Style Scrolling Action Keystrokes Equivalents ────────────────────────────────────────────────────────────────────────── Beginning of line HOME CTRL+Q+S End of line END CTRL+Q+D Page up PGUP CTRL+R Page down PGDN CTRL+C Left one window CTRL+PGUP --- Right one window CTRL+PGDN --- Beginning of file CTRL+HOME CTRL+Q+R End of file CTRL+END CTRL+Q+C ────────────────────────────────────────────────────────────────────────── You can also set place markers anywhere in your program and jump between them while editing. See Chapter 12, "Using the Editor," for more information. 10.5 Using the Immediate Window The Immediate window, the bottom window on the initial QuickBASIC screen, allows direct execution of QuickBASIC statements. Use it to refine short pieces of program code and see the effect immediately. When you are satisfied with the results, you can copy the code into your program. Figure 10.7 shows code being tested in the Immediate window. File Edit View Search Run Debug Calls Options Help DEMO2.BAS NUM: DEMO2.BAS TOTAL: ┌─────────────────────────────── DEMO2.BAS ───────────────────────────┤├── │DECLARE SUB Bounce (Hi%, Low%) │DECLARE SUB Fall (Hi%, Low%, Del%) │DECLARE SUB Siren (Hi%, Rng%) │DECLARE SUB Klaxon (Hi%, Low%) │DEFINT A-Z │' QB2 Version of Sound Effects Demo Program │' (works under most other BASIC compilers) │ │' Sound effects menu │WHILE Q$ <> "Q" │ CLS ├─────────────────────────────── Immediate ──────────────────────────────── │LOCATE 4,5 : PRINT "TEST" ││ ││ │<Shift+F1=Help> <F6=Window> <Enter=Execute Line> 00001:026 │ Code being tested Figure 10.7 Immediate Window You can enter up to ten separate lines in the Immediate window, then move among them with the DIRECTION keys. Each line is limited to 256 characters. Multiple statements are permitted on one line, but each complete statement must be separated from the next by a colon (:). When you place the cursor on a line and press ENTER, only the statements on that line execute. As you write your program, you can make the Immediate window active, type and edit statements as you would in the Edit window, then execute them immediately. By testing your ideas before incorporating them into a larger program, you verify that they function properly. The Immediate window is similar to "direct mode" in BASICA, and has the following characteristics: ■ Any statement or group of statements on a line will be executed when you place the cursor anywhere on the line and press ENTER. ■ As many as ten lines can be entered in the Immediate window; you can execute the lines in any order. After you have entered ten lines, each new line scrolls the text in the Immediate window up one line. ■ A line can have a maximum of 256 characters. Statements can be grouped on a line, but must be separated by colons (:). ■ Each line is executed independently of all other lines in the window. However, changes in one line can affect other lines. For example, the following lines contain two assignments to the integer variable x%, so the value printed by the second line corresponds to whichever assignment line was most recently executed: x% = 5 print x% x% = 9 ■ The Immediate window is expanded when you repeatedly press ALT+PLUS while it is the active window. Pressing CTRL+F10 while the Immediate window is active expands it to the full screen, but no matter how many lines appear, only the first ten are available for use. Press CTRL+F10 again to return the window to its previous size. ■ Code written in the Immediate window is not saved to disk by the Save command. Use the Cut or Copy commands from the Edit menu to move the contents of the Immediate window into a View window if you want to save them with the rest of the file. See Also Section 17.2, "Preventing Bugs with QuickBASIC"; Section 17.3.5, "Immediate Window" 10.5.1 Statements Not Allowed Most QuickBASIC statements and functions are allowed in the Immediate window. However, an error message will appear if you use the following QuickBASIC keywords in the Immediate window: ────────────────────────────────────────────────────────────────────────── COMMON ELSEIF OPTION CONST END DEF REDIM DATA END FUNCTION SHARED DECLARE END IF $STATIC DEF FN END SUB STATIC DEFtype END TYPE SUB DIM FUNCTION TYPE DYNAMIC $INCLUDE $DYNAMIC ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── NOTE Although the END IF statement is not allowed in the Immediate window, you can still use the single-line form of IF...THEN...ELSE there. ────────────────────────────────────────────────────────────────────────── 10.5.2 Doing Calculations Use the Immediate window to calculate complicated expressions, then display results with the PRINT statement. Use any of BASIC's intrinsic functions (such as SIN or EXP) in these calculations. Similarly, you can use the Immediate window to print the value returned by FRE(-1). This tells you the amount of memory available after both QuickBASIC and your program are loaded. 10.5.3 Testing Screen Output As a program grows in length and complexity, it is useful to test your code before incorporating it into your program. Typing code in the Immediate window and testing it there first avoids having to run a program from the beginning each time you want to modify a small part of code. Examples You can use the following lines in the Immediate window to test the position at which output will be written to the screen: row% = 1 : col% = 4*row% : LOCATE row%,col% : PRINT "." By changing the value of the variable row%, then pressing ENTER, you can position the period in the PRINT statement in different places on the screen. Sometimes a program can leave the output screen in an undesirable mode when it finishes running (for example, a graphics program may end without resetting the screen to 80-column text mode). If this happens, use the Immediate window to put the screen in the output mode you want. For example, the following lines restore the output screen to 80-column text mode and close any text viewport (a restricted horizontal slice of the screen) set in the program: screen 0 width 80 view print 10.5.4 Invoking Procedures You can isolate the effects of any individual SUB or FUNCTION procedure by calling it from the Immediate window. Use the Immediate window to execute only those statements between the SUB and END SUB or FUNCTION and END FUNCTION statements. For example, entering the following line in the Immediate window executes all statements in the procedure SubProgram1, including any calls it makes to other procedures: call SubProgram1 10.5.5 Changing the Values of Variables Use the Immediate window to assign a new value to a variable in a running program. Stop the program, assign the variable a new value in the Immediate window, and continue execution. The value you assign in the Immediate window becomes the variable's value when the program continues running. Example The following steps show how you can use the Immediate window to change a variables in a running program: 1. Type this program in the View window: FOR i% = 0 TO 10000 LOCATE 10, 20 : PRINT i% LOCATE 10, 27 : PRINT " and still counting" NEXT i% 2. Use the Start command on the Run menu to start the program, then use CTRL+BREAK to interrupt it. 3. Type i% = 9900 in the Immediate window and press ENTER. 4. Press F5 to continue the program. The loop now executes from 9900 to 10,000. The Immediate window can access variable values only after those variables have been assigned values; this occurs after statements containing the variables have been executed in the View window. For example, suppose the statement you just executed in the View window gave a variable called x% a value of 3. You then enter PRINT x% in the Immediate window. The number 3 will be printed to the screen when you press ENTER. Similarly, if the next statement to be executed in the View window is a module-level statement, you cannot access the variables of a SUB or FUNCTION from the Immediate window. 10.5.6 Simulating Run-Time Errors Run-time errors are those that occur while a program is running. Each run-time error is associated with a numeric code. If your program uses error handling (ON ERROR statements), QuickBASIC returns this numeric code to your program. One way to find out which error message is associated with a given code is to refer to Appendix I, "Error Messages," in Programming in BASIC. Another way is to simulate the error itself. You can simulate an error by moving to the Immediate window and entering the given number as an argument to the ERROR statement. QuickBASIC then displays the dialog box for that error, as if the error had actually occurred in a running program. Figure 10.8 shows an error-message dialog box on the QuickBASIC screen. Error-message dialog box │ File Edit View Search │Run Debug Calls Options Help ┌───────────────────────────┼─── DEMO1.BAS ───────────────────────────┤├── │5 DEFINT A-Z │ │10 ' BASICA/GWBASIC Version│of Sound Effects Demo Program │15 ' │ │20 ' Sound effect menu │ │25 Q = Z │ │30 WHILE Q >= 1 │ │35 CLS │ │40 PRINT "Sound effect┌┼──────────────────────┐ │45 COLOR 15, 0: PRINT ││ │ "ouncing" │50 COLOR 15, 0: PRINT │ File already exists │ "alling" │55 COLOR 15, 0: PRINT │ │ "laxon" │60 COLOR 15, 0: PRINT ├───────────────────────┤ "iren" │65 COLOR 15, 0: PRINT │ < OK > < Help > │ "uit" │70 PRINT : PRINT "Sele└───────────────────────┘ │75 Q$ = INPUT$(1): Q = I Get valid key │80 IF Q = 0 GOTO 75 │85 CLS ' Take action based on key ├─────────────────────────────── Immediate ──────────────────────────────── │error 58 ││ ││ │<Shift+F1=Help> <F6=Window> <Enter=Execute Line> C 00001:001 │ Error code entered in Immediate window Figure 10.8 Simulated Run-Time Error 10.6 Using the Watch Window The Watch window is one of QuickBASIC's advanced debugging features. It displays variables tracked for debugging purposes. The Watch window opens at the top of the screen when you set a watchpoint or add a watch expression. (See Section 17.3.2, "Breakpoints and Watchpoints," and Section 17.3.3, "Watch Expressions.") Figure 10.9 shows the QuickBASIC screen with entries in the Watch window. Location where you added the variable ┌───Variables (or expressions) Values (or conditions │ │ │ │ File Edit │View Search Run Debug Calls Options │ Help │TEST.BAS I:─┤1────────────────────────────────────────┤ └TEST.BAS J:─┘12───────────────────────────────────────┘ ┌──────────────────────────────── TEST.BAS ───────────────────────────┤├── │FOR I = 1 TO 900 │ FOR J = 1 TO 600 │ PRINT I │ PRINT J │ NEXT J │NEXT I │END │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── DEMO1.BAS ───────────────────────────┤├── │5 DEFINT A-Z │10 ' BASICA/GWBASIC Version of Sound Effects Demo Program │15 ' │20 ' Sound effect menu │25 Q = Z │30 WHILE Q >= 1 │35 CLS │40 PRINT "Sound effects": PRINT ├─────────────────────────────── Immediate ──────────────────────────────── │LOCATE 4,5 : PRINT "TEST" │ <Shift+F1=Help> <F5=Continue> <F9=Toggle Bkpt> <F8=Step> C 00004:007 Figure 10.9 Watch Window The Watch window opens whenever you choose the Add Watch or Watchpoint command, or when you choose Add from the Instant Watch dialog box. Add Watch, Watchpoint, and Instant Watch are all on the Debug menu. Each Watch window entry contains the following information: ■ Location where you added the variable. This part of the entry names the module or procedure from which you added an expression to the Watch window. ■ Variable or expression. The variable or expression you want to track. ■ Value or condition. In Figure 10.9, the variables I and J have values 1 and 12, respectively. Since the program is currently executing in TEST.BAS and both I and J were added to the Watch window when TEST.BAS was in the View window (indicated by the TEST.BAS entry in front of both I and J), both of their values appear. If they had been added from a different location such as a procedure, then the procedure name would appear in the Watch window and Not watchable would appear in the value location while the program executed in TEST.BAS. See Also Section 17.3.4, "Watch Window"; Chapter 18, "The Debug Menu" 10.7 Using the Mouse You can use QuickBASIC with a mouse. Terms associated with the mouse and used in this manual include the following: Mouse Term Description ────────────────────────────────────────────────────────────────────────── Mouse cursor Block cursor that moves on the screen as you move the mouse. Click Placing the mouse cursor on an item, and pressing and releasing the left mouse button. Double click Placing the cursor on an item and pressing the left mouse button twice in a row. Drag Placing the mouse cursor at the beginning of what you wish to select. Press the left mouse button and hold it down. Move the pointer to the end of your desired selection and release the button. Use this technique to highlight words, manipulate window sizes, and use scroll bars. ────────────────────────────────────────────────────────────────────────── To choose commands with the mouse follow these steps: 1. Point to the menu name and click the left mouse button. 2. Point to the command you want to select and click the left mouse button. ────────────────────────────────────────────────────────────────────────── NOTE Use only the left mouse button to choose QuickBASIC menus or commands. Clicking the right mouse button is the same as pressing F1 (accessing on-line help). For information on how to set the right mouse button to execute your program to the line containing the mouse cursor, see Section 20.3, "Right Mouse Command." ────────────────────────────────────────────────────────────────────────── Table 10.3 explains mouse techniques for accomplishing other tasks. Table 10.3 Mouse Commands ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Task Mouse Technique ────────────────────────────────────────────────────────────────────────── Close a menu Move the mouse cursor off the menu and click the left button. Make a window active Click anywhere in the window. Expand or shrink a View Move the mouse cursor to the title bar and drag or Immediate window the title bar up or down. Expand the active window Click the maximize box, at the right of the title to occupy the full bar, or double click the mouse anywhere on the screen title bar. Scroll text Place the cursor on the scroll box and drag it to a position on the bar that corresponds to the general location in the file you want. Task Mouse Technique ────────────────────────────────────────────────────────────────────────── general location in the file you want. To scroll one page at a time, place the mouse cursor in the scroll bar between the scroll box and the top or bottom of the scroll bar and click the left button. To scroll one line or one character at a time, click the scroll arrows at either end of the scroll bars. Select programs and Double click the file name, click the file name files and OK in a list box (use this technique with the Open Program, Merge, and Load File commands), or single click to highlight the file name and press ENTER. Change directories Double click a directory name to view its contents. (In most dialog boxes, directories and Task Mouse Technique ────────────────────────────────────────────────────────────────────────── contents. (In most dialog boxes, directories and drives appear in a separate list to the right of the file list.) If the current directory is a subdirectory, two periods (. .) appear in the list. Double click the two periods to move up one directory level. Display Instant Watch Press and hold the SHIFT key while clicking the dialog box right mouse button. ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── NOTE To open a program with the mouse, double click the file name in the list box. Clicking an item with a mouse selects that item. Double clicking an item in a list box selects the item, confirms all previous choices, and closes the dialog box. ────────────────────────────────────────────────────────────────────────── 10.8 Using On-Line Help QuickBASIC has an extensive on-line help system. Through on-line help, you can get information on virtually any QuickBASIC topic, menu, command, or keyword. See Also Chapter 21, "The Help Menu" 10.8.1 Help Features QuickBASIC's on-line help consists of two parts: environment help (for error messages, menus, and commands) and the Microsoft QB Advisor (for language-oriented topics). Press ESC to clear either type of on-line help from your screen. Environment help appears in dialog boxes; the QB Advisor appears in the Help window at the top fo the screen. The following special features are available within the QB Advisor: ■ Hyperlinks connect related topics; they give you immediate access to all related information on a particular topic (see Section 10.8.2). ■ Examples can be copied or pasted directly into your program. You may resize the Help window, use commands such as PGUP and the DIRECTION keys, and scroll. You can even use Find from the Search menu to locate specific information within a particular help screen. ■ Placemarkers can be used. If you use a particular screen frequently, set a placemarker there as you would in program text. Later, you can quickly return to the same screen. (See Section 12.4, "Using Placemarkers in Text.") ■ QuickBASIC remembers up to the last 20 hyperlinks you accessed. Rather than repeatedly search through on-line help, you can press ALT+F1 to trace back through as many as 20 help screens. You can access on-line help in four ways: 1. Move the cursor to the word in your program you want help on, and press F1. 2. Select the Help button or press F1 when a help dialog box is displayed. 3. Use hyperlinks from within Help windows to call up more information on related topics (see Section 10.8.2). 4. Select a command from the Help menu. 10.8.2 Hyperlinks The QB Advisor provides interconnections called "hyperlinks" between related subjects. With a few keystrokes, you can access all of the information and related material on a particular topic. Hyperlinks appear at the top and bottom of the Help window between highlighted (on monochrome monitors) or green (on most color monitors) triangles. Any BASIC keyword also forms a hyperlink to that keyword's on-line help. To use a hyperlink, make the Help window active (press SHIFT+F6), and press the TAB key to move the cursor to the hyperlink you want to activate. Alternatively, you can enter the first letter of a hyperlink's name and the cursor will jump to that hyperlink. Press F1 to call up the screen associated with that hyperlink. ────────────────────────────────────────────────────────────────────────── NOTE Mouse users can place the mouse cursor on a hyperlink and click the right button, provided the right button function is set to invoke context-sensitive help (the default setting). ────────────────────────────────────────────────────────────────────────── Figure 10.10 shows examples of hyperlinks in the PRINT Help screen. The Remarks and Example hyperlinks provide additional remarks and examples. Inactive hyperlink (screen currently Hyperlinks to additional Hyperlinks to displayed) ┌─ help on PRINT general help topics │ │ ┌────┴────┐ │ File Edit View│ Search Run Debug Options │ │ Help ┌┼─────────────────┼── HELP: PRINT Statement QuickSCREEN ├─────────┼──┤├── │└ QuickSCREEN │ Details Example Contents Index │───────────────── └────┴──────────────┘ ───────────────────────────────── │PRINT - a device I/O statement that outputs data on the screen │ │Syntax │ PRINT [expressionlist][{,|;}] │ │ ■ If expressionlist is omitted, a blank line is printed. │ ■ If expressionlist is included, the values of the expressions are │ printed on the screen. │ ■ The expressions in the list may be numeric or string expressions. │ (String literals must be enclosed in quotation marks.) │ │Other Uses of the PRINT Keyword │ ┌PRINT USING - to output formatted text to the screen │ │PRINT # - to output data to a sequential file ││▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ │ Hyperlinks to related statements Figure 10.10 Help on the PRINT Statement 10.8.3 Moving in Help Windows You can use the keyboard to move in Help windows. For example, you can use the DIRECTION keys. You can also use the key sequences described in Table 10.4. Table 10.4 Help Keys ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Key Sequence Description ────────────────────────────────────────────────────────────────────────── SHIFT+F1 Displays Help on Help ESC Clears help from the screen TAB Moves to next hyperlink SHIFT+TAB Moves to previous hyperlink Key Sequence Description ────────────────────────────────────────────────────────────────────────── character Moves to next hyperlink starting with the letter character SHIFT+character Moves to previous hyperlink starting with the letter character PGUP Displays previous screen (if one exists) of current topic PGDN Displays next screen (if one exists) of current topic CTRL+F1 Displays help for the topic stored just after the current help topic SHIFT+CTRL+F1 Displays help for the topic stored just before the current help topic ────────────────────────────────────────────────────────────────────────── Key Sequence Description ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── 10.8.4 Help Files When you choose any help command, QuickBASIC searches for the appropriate help file. QuickBASIC searches the current working directory, then the directory specified by the Set Paths command (Options menu), and finally any removable disks present in your system. If QuickBASIC cannot find an appropriate file, it displays the dialog box shown in Figure 10.11. Copy the missing file into the appropriate directory. ┌───────────────────────────────────────────────────────┐ │ │ │ File QB45QCK.HLP not found. │ │ Put the floppy disk with this file into the drive and │ │ Retry, or change your Help path in Options+Set Paths. │ │ │ ├───────────────────────────────────────────────────────┤ │ < Retry > < Cancel > │ └───────────────────────────────────────────────────────┘ Figure 10.11 Dialog Box for Missing Help File If you cannot invoke any form of on-line help, you may be missing all of the help files; in this case, you need to check the contents of your QuickBASIC directory or rerun the setup procedure. Or you may have inadequate memory to display on-line help. This situation can occur if you try to run QuickBASIC concurrently with other memory-resident files. In this case, remove one or more memory-resident files and start QuickBASIC again. You may also have inadequate memory if your machine doesn't meet the minimum system requirements (see the introduction to this manual). 10.8.5 Hard-Disk System If you use a hard disk, you installed all of the help files in a single directory during your setup (see Chapter 1, "Setting Up Microsoft QuickBASIC," for more information). The Set Paths command on the Options menu specifies the directory path to the help files. When you invoke language-oriented help, you will automatically receive the QB Advisor. 10.8.6 Removable-Disk System Microsoft QuickBASIC provides some language help on the same disk that contains QuickBASIC. This file contains statement descriptions and syntax, but not the detailed examples available in the QB Advisor. To use the QB Advisor on a dual removable-disk system, press either the Remarks or Example hyperlinks at the top of the screen. A dialog box asks you to insert the Microsoft QB Advisor disk. Once you insert the Microsoft QB Advisor disk, you can access more detailed help on QuickBASIC's keywords. You may leave the Microsoft QB Advisor disk in the drive until QuickBASIC prompts you for another disk. ──────────────────────────────────────────────────────────────────────────── Chapter 11 The File Menu The File menu lets you work with files in QuickBASIC. From the File menu you can create new files, load existing files, modify files, or remove files. You also use the File menu to print files and exit from QuickBASIC. The File menu has the following commands: ■ New Program. Clears any previously loaded program and lets you begin a new program. ■ Open Program. Opens a program; lists system files and directories. ■ Merge. Merges the contents of two files (Full Menus only). ■ Save. Writes the contents of the file in the active View window to a disk file (Full Menus only). ■ Save As. Saves the current file with the name you specify. ■ Save All. Saves all currently loaded files (Full Menus only). ■ Create File. Begins either a new program module, an include file, or a document file as part of the current program (Full Menus only). ■ Load File. Loads an existing file──either a program module, an include file or a document file──into memory (Full Menus only). ■ Unload File. Removes an entire file from memory (Full Menus only). ■ Print. Lets you print all or part of your program. ■ DOS Shell. Returns temporarily to the DOS command level (Full Menus only). ■ Exit. Removes program from memory and returns to the DOS prompt. 11.1 New Program Command The New Program command from the File menu clears all previously loaded files so you can begin typing a completely new program. If a loaded program contains unsaved text, QuickBASIC asks if you want to save it before clearing it from memory. A program contains one or more BASIC statements that QuickBASIC will translate into instructions for your computer. BASIC programs can be contained in a single file. However, QuickBASIC also allows you to build programs containing multiple self-contained parts ("modules"). Each module usually contains procedures that are used to perform specific tasks. One such module may be called into several programs. The New Program command creates the main module of a multiple-module program. In a single-module program, the main module is the only module. A program can have four types of files: ■ One main module (required) ■ Other modules ■ Include files ■ Document files (including .MAK files) Modules can contain the following: ■ Module-level code ■ SUB procedures ■ FUNCTION procedures ────────────────────────────────────────────────────────────────────────── NOTE When you are writing a completely new program, use the New Program command. When you are calling up a program that already exists on disk, use the Open Program command. ────────────────────────────────────────────────────────────────────────── See Also Section 11.2, "Open Program Command"; Section 11.7, "Create File Command" 11.2 Open Program Command The Open Program command opens an existing program. The dialog box displayed initially lists the files with .BAS extensions in the current working directory. You can also list files in other directories and on other disks on your system. When you choose the Open Program command, the dialog box shown in Figure 11.1 appears. Path of currently Entry determines which Symbol for next loaded file files are displayed highest directory ┌┼────────────────────┼─────── Open Program ───────────┼─────────────────── ││ ┌────────┼────────────────────────────────┼─────────────────┐ ││File Name: │*.BAS │ │ ││ └─────────────────────────────────────────┼─────────────────┘ │└C:\QB4.5\DEMO │ │ Files │ Dirs/Drives │ ┌──────────────────────────────────────────────────┐ │ ┌───────────────┐ │ │ ATEST.BAS TEST.BAS ─┐ │ └─┼─.. │ │ BL.BAS TORUS.BAS │ │ │ SOURCE ─┐ ▒ │ │ DEMO1.BAS VARHELP.BAS │ │ │┌[-A-] │ ▒ │ │ DEMO2.BAS VARHELP2.BAS │ │ ┌┼┤[-B-] │ ▒ │ │ DEMO3.BAS ├─────┐ │ ││└[-C-] │ ▒ │ │ QBFORMAT.BAS │ │ │ ││ │ ▒ │ │ QCARDS.BAS │ │ │ ││ │ ▒ │ │ REMLINE.BAS │ │ │ ││ │ ▒ │ │ SORTDEMO.BAS ─┘ │ │ ││ │ │ └▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒┘ │└─────────┼─────┘ ├─────────────────────────────────────────┼─────────────┼──────────┼─────── │ < OK > < Cancel > │ < Help >│ │ └─────────────────────────────────────────┼─────────────┼──────────┼─────── │ │ │ .BAS files in current directory Drives Subdirectory Figure 11.1 Open Program Dialog Box If a program consists of several modules, all of the modules belonging to the program are loaded. If a program uses include files (see Section 2.5.4.3, "Using Include Files for Declarations," and Appendix F, "Metacommands," in Programming in BASIC), the include files are compiled, but not loaded or displayed. 11.2.1 Specifying a File Files are displayed in columns in the Files list box. Directories and available drives appear in the Dirs/Drives list to the right of the Files list. Use the DIRECTION keys or the scroll bars to scroll in either of the list boxes. Note that the Files list box scrolls left and right, and the Dirs/Drives list box scrolls up and down. The Open Program dialog box provides two ways to specify the file you want to load (see Section 10.7, "Using the Mouse," for mouse techniques). Use either of the following two methods: 1. Type the name of the program in the text box and press ENTER. If you enter a file name with no extension, QuickBASIC assumes your file has the .BAS extension. If you want to load a file that has no extension, type a period (.) immediately after the file name. 2. Press the TAB key to move to the list box, and use the DIRECTION keys to move through the list box until the desired file is highlighted. Then press ENTER. You can also highlight the file name by moving to the list box and pressing the first letter of the name of the file you want to load. In either case, the text of the program appears in a window with the file name in the title bar. 11.2.2 Listing Directory Contents You can use the Open Program dialog box to list the contents of any directory on your system. When you choose a directory name in the Dirs/Drives list box, QuickBASIC lists all the subdirectories and .BAS files in the directory you choose. When you enter or choose a file name from the Files list box, that file is loaded into memory. The following list describes several methods you can use to list contents of directories: Task Action ────────────────────────────────────────────────────────────────────────── Listing all files in the current Type *.* in the text box. directory Listing files in root directory of Type A:*.* in the text box. drive A Listing all files in a subdirectory Highlight BIN in the Dirs/Drives list named BIN box and press ENTER. Type *.* in the text box. Listing all files in the current Type *.BI in the text box. directory with the .BI extension Listing all files in the directory Type .. in the text box. Or, press a immediately above the current DIRECTION key or the period (.) to directory select .. if you are already in the Dirs/Drives list box. Then type *.* in the text box. ────────────────────────────────────────────────────────────────────────── ────────────────────────────────────────────────────────────────────────── NOTE The "current working directory" is the directory shown by the CD command from DOS. In contrast, when you select a directory from a list box, you are only listing the files it contains, not changing the current working directory at the DOS level. If you want to change the current working directory, make the Immediate window active, and use the CHDIR statement. ────────────────────────────────────────────────────────────────────────── See Also Section 11.1, "New Program Command"; Section 11.8, "Load File Command" 11.3 The Merge Command (Full Menus Only) The Merge command on the File menu inserts the contents of a file at the beginning of the line the cursor is on. When you choose the Merge command from the File menu, the dialog box shown in Figure 11.2 appears. Path of currently Entry determines which Symbol for next loaded file files are displayed highest directory ┌┼────────────────────┼────────── Merge ───────────────┼─────────────────── ││ ┌────────┼────────────────────────────────┼─────────────────┐ ││File Name: │*.bas │ │ ││ └─────────────────────────────────────────┼─────────────────┘ │└C:\QB4.5\DEMO │ │ Files │ Dirs/Drives │ ┌──────────────────────────────────────────────────┐ │ ┌───────────────┐ │ │ ATEST.BAS TEST.BAS ─┐ │ └─┼ .. │ │ BL.BAS TORUS.BAS │ │ │ SOURCE ─┐ ▒ │ │ DEMO1.BAS VARHELP.BAS │ │ │┌[-A-] │ ▒ │ │ DEMO2.BAS VARHELP2.BAS │ │ ┌┼┤[-B-] │ ▒ │ │ DEMO3.BAS ├─────┐ │ ││└[-C-] │ ▒ │ │ QBFORMAT.BAS │ │ │ ││ │ ▒ │ │ QCARDS.BAS │ │ │ ││ │ ▒ │ │ REMLINE.BAS │ │ │ ││ │ ▒ │ │ SORTDEMO.BAS ─┘ │ │ ││ │ │ └▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒┘ │└─────────┼─────┘ ├─────────────────────────────────────────┼─────────────┼──────────┼─────── │ < OK > < Cancel > │ < Help >│ │ └─────────────────────────────────────────┼─────────────┼──────────┼─────── │ │ │ .BAS files in current directory Drives Subdirectory Figure 11.2 Merge Dialog Box The Merge dialog box operates the same way as the Open Program dialog box. However, the Merge command inserts the specified file into the current file, whereas the Open Program command clears whatever is currently in memory, then loads the program. ────────────────────────────────────────────────────────────────────────── NOTE QuickBASIC cannot merge binary files; the file brought in with the Merge command must be text format. ────────────────────────────────────────────────────────────────────────── See Also Section 11.2, "Open Program Command," and Section 14.1, "SUBs Command," in this manual; Chapter 7, "Programming with Modules," and Appendix B, "Differences from Previous Versions of QuickBASIC," in Programming in BASIC. 11.4 Save Command (Full Menus Only) The Save command saves the contents of the current file (the file being displayed in the active View window) to a disk file. If the file you are saving already has a name, Save overwrites the version on disk. If the file does not have a name, the Save dialog box in Figure 11.3 appears to ask you for a name. Path of currently File name Subdirectory loaded file │ │ ┌┼────────────────────┼──┼ Save ───────────────────────┐ ││ ┌────────┼──┼───────────────────────────┐ │ ││File Name: │CALC.BAS │ │ │ ││ └───────────┼───────────────────────────┘ │ │└C:\QB4.5\DEMO │ │ │ Dirs/Drives │ │ │ │ │ │ ┌───────────────┐ ┌──┼──────── Format ───────────┐ │ │┌┼ .. │ │ (∙) QuickBASIC - ─┐ │ │ │││ SOURCE ───────────┼──┘ Fast Load and ├───┐ │ │ │││ [-A-]─┐ ▒ │ Save ─┘ │ │ │ │││ [-B-] ├────┐ ▒ │ │ │ │ │││ [-C-]─┘ │ ▒ │ ( ) Text - ─┐ │ │ │ │││ │ ▒ │ Readable by ├──│ │ │ │││ │ │ Other Programs ┘ │ │ │ ││└────────────┼──┘ └───────────────────────────┼──┘ │ ├┼─────────────┼──────────────────────────────────┼────┤ ││ < OK > │ < Cancel > < Help >│ │ └┼─────────────┼──────────────────────────────────┼────┘ Symbol for │ │ next highest Drives File-format options directory Figure 11.3 Save Dialog Box See Also Section 11.5, "Save As Command"; Section 11.6, "Save All Command" 11.5 Save As Command The Save As command saves the current file with the name you specify. It is useful for saving a file under a new name and changing the format in which the file is saved. If you change the name, the old file still exists with the name it had the last time it was saved. When you choose Save As from the File menu, a dialog box like that shown in Figure 11.3 appears. The Save As dialog box lists the existing name of the file you want to save. Enter a new name in the text box to replace the old name. The next time you save the file, the new file name will appear in the text box. The following list describes the file-format options in the Save dialog box: Option Purpose ────────────────────────────────────────────────────────────────────────── QuickBASIC──Fast Load Saves a program in QuickBASIC format. A program and Save saved this way loads faster than one saved as a text file but can be edited only using QuickBASIC. Because it is a non-ASCII file, you will not be able to change it using another text editor. This is QuickBASIC's default format for saving a program. Files classified as document or include files with the Create File or Load File command cannot be saved in this format. Text──Readable by Other Saves your file to disk as a text (ASCII) file. Programs Text files can be read, modified, or printed by any editor or word processing program that reads ASCII files. Files classified as document or include files are always stored in this format. ────────────────────────────────────────────────────────────────────────── See Also Section 11.4, "Save Command"; Section 11.6, "Save All Command" 11.6 Save All Command (Full Menus Only) The Save All command saves all currently loaded files that have changed since the last time you saved a file. A currently loaded file is one whose name appears in the dialog box of the View menu's SUBs command. Save All is useful when you are working with multiple files in memory. If the main module you are saving already has a name, Save All overwrites the version on disk. If the main module does not have a name, a dialog box like that shown in Figure 11.3 asks you for a name. Section 11.5 explains each of the file-format options. When you save a multiple-module program, QuickBASIC creates a special file on your disk that contains the names of all the modules in the program. The file is given the base name of the main module plus the extension .MAK. QuickBASIC uses the .MAK file as a roadmap to the various program modules the next time you load the program. For more information on .MAK files, see Section 16.7.2. See Also Section 11.4, "Save Command"; Section 14.1, "SUBs Command" 11.7 Create File Command (Full Menus Only) The Create File command on the File menu allows you to begin a new file as part of the program currently in memory. When you choose the Create File command from the File menu, a dialog box appears. To create a new file, type the file name in the text box, select the file type, and press ENTER. See Figure 11.4. File name │ ┌────────────┼──── Create File ──────────────────┐ │ ┌────┼─────────────────────────────────┐ │ │ Name: │CALC.BAS │ │ │ └──────────────────────────────────────┘ │ │┌──┬──────────────┬───────────────┐ │ ││ (∙) Module ( ) Include ( ) Document │ ├┼───────────────────────────────────────────────┤ ││ < OK > < Cancel > < Help > │ └┼───────────────────────────────────────────────┘ │ File-type options Figure 11.4 Create File Dialog Box Select the appropriate file type from the following: ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ File Type Description ────────────────────────────────────────────────────────────────────────── Module A discrete program component. A program consists of at least one module. When you make a program out of several modules, each module is saved on disk as a separate file when you save the File Type Description ────────────────────────────────────────────────────────────────────────── disk as a separate file when you save the program. Modules are handy if you have long programs or use the same groups of procedures over and over in different programs. QuickBASIC's smart editor checks syntax and formatting in modules. See Section 12.5 in this manual for information on the smart editor. See Chapter 7 in Programming in BASIC for more information on modules. Include A text file whose statements are compiled into your program when QuickBASIC encounters the file's name following a $INCLUDE metacommand. QuickBASIC's smart editor checks syntax and formatting in include files as it does in modules. Although the contents of the include file are used in your program, the include file itself is not a part of the program. Its name File Type Description ────────────────────────────────────────────────────────────────────────── itself is not a part of the program. Its name does not appear in the .MAK file of a multiple-module program. Document A text file. QuickBASIC does not treat a file opened as a document as BASIC code, so the smart editor does not check document files for syntax and formatting. However, you can edit a document file with the QuickBASIC editor just as you would with a normal word processor. Document file names never appear in the .MAK file of a multiple-module program. ────────────────────────────────────────────────────────────────────────── Once you have created any of the preceding kinds of files in QuickBASIC, you can see the file's name in the list box of the View menu's SUBs dialog box. While a file's name appears in this list box, you cannot load it again, even with a different classification. For example, if you create a file as a document, you cannot load it again as an include file until you unload the current copy with the Unload File Command (see Section 11.9, "Unload File Command"). ────────────────────────────────────────────────────────────────────────── NOTE Use the Create File command to add a new module to the program currently in memory. Create File differs from Open Program, which loads a file as a module after unloading all other files prior to loading the program. If no other modules are loaded when you use Create File to create a module, it is considered the main module of the program. ────────────────────────────────────────────────────────────────────────── See Also Section 11.1, "New Program Command"; Section 11.2, "Open Program Command"; Section 11.8, "Load File Command"; Section 14.1, "SUBs Command" 11.8 Load File Command (Full Menus Only) The Load File command on the File menu loads single program modules──as well as include files and document files──from disk into memory. When you choose Load File, a dialog box appears. To load a file, type the file name in the text box, select the file type, and press ENTER. See Figure 11.5. Path of currently File to load .BAS files in loaded file │ current directory ┌┼────────────────────┼──────── Load File ─────┼─────────────────────────── ││ ┌────────┼────────────────────────┼─────────────────────────┐ ││File Name: │DEMO1.BAS │ │ ││ └─────────────────────────────────┼─────────────────────────┘ │└C:\QB4.5\DEMO │ │ Files │ Dirs/Drives │ ┌────────────────────────────────────────────┼─────┐ ┌───────────────┐ │ │ ATEST.BAS SORTDEMO.BAS ─┐ │ │ │ .. │ │ BL.BAS TEST.BAS │ │ │ │ SOURCE ▒ │ │ DEMO1.BAS TORUS.BAS │ │ │ │ [-A-] ▒ │ │ DEMO2.BAS VARHELP.BAS │ │ │ │ [-B-] ▒ │ │ DEMO3.BAS VARHELP2.BAS ├──────────┘ │ │ [-C-] ▒ │ │ QBFORMAT.BAS │ │ │ ▒ │ │ QCARDS.BAS │ │ │ ▒ │ │ REMLINE.BAS ─┘ │ │ │ └▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒┘ └───────────────┘ │ ┌────────────┬───────────┬────────────┐ │ │ Load as: (∙) Module ( ) Include ( ) Document ├─┼──────────────────────────────────────────────────────────────────────── │ │ < OK > < Cancel > < Help > └─┼──────────────────────────────────────────────────────────────────────── │ File-type options Figure 11.5 Load File Dialog Box You must select the correct file type: Module, Include, or Document. See Section 11.7, "Create File Command," for more details on specific file types. Once you have loaded any type of file into QuickBASIC, you can see the file name in the list box of the View menu's SUBs dialog box. While a file name appears in this list box, you cannot load it again, even with a different classification. For example, if you load a file as a document, you cannot load it again as an include file until you unload it with the Unload File command. See Section 11.9 for more information on Unload File. If you have procedures in other modules (program files) that you want to use in the current program, you can load those modules using Load File. Once the file is loaded, you can reference the procedures it contains anywhere in the current program. Modules from other programs can be added into the program currently in memory as follows: 1. Choose the Load File command from the File menu. 2. Select the name of the module containing procedures you want to use in the current program. 3. Press ENTER to load the file as a module, since the Module option is already chosen. 4. Repeat steps 1-3 for each module you want to load. Save the program using the Save All command once all the modules are loaded. See Also Section 11.1, "New Program Command"; Section 11.7, "Create File Command" 11.9 Unload File Command (Full Menus Only) The Unload File command removes an include file, document, or entire module from memory. After you unload a module, the disk file containing the module still exists; however, when you save your program, the module is no longer a part of the program. If your program contains more than one module, the name of the unloaded module is removed from the program's .MAK file. If you unload the main module of a multiple-module program, QuickBASIC prompts you to set a new main module before proceeding. Unloading a document or include file leaves any other loaded files in memory. When you choose the Unload File command, the dialog box shown in Figure 11.6 appears. File to unload ┌────────── Unload File ──────────┐ │ Choose module to unload: │ │ ┌───────────────────────────┐ │ │ │ DEMO1.BAS │ │ │ DEMO2.BAS ▒ │ │ │ TEST.BAS ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ │ │ └───────────────────────────┘ │ │ │ ├─────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └─────────────────────────────────┘ Figure 11.6 Unload File Dialog Box Follow these steps to unload a file: 1. Choose the Unload File command from the File menu. 2. Select the name of the module, include file, or document that you no longer want in the program. 3. Press ENTER. The module is unloaded but still exists as a disk file. You can use Unload File to unload any type of file──a program module, include file, or document file──from memory. See Also Section 11.1, "New Program Command"; Section 16.7.2, "The .MAK File" 11.10 The Print Command The Print command on the File menu lets you print selected text, text in the active window, the entire current module, or all currently loaded program modules. To use the Print command, your printer must be connected to your computer's LPT1 port. When you choose the Print command from the File menu, the dialog box shown in Figure 11.7 opens. Select the appropriate option from the Print options box to print your file. Prints Prints contents of selected text active window │ │ ┌─────────┼─ Print ─────────┼──┐ │ │ │ │ │ ( ) Selected Text │ │ │ ( ) Active Window─────┘ │ │ ( ) Current Module──────┐│ │ ( ) All Modules ││ │ │ ││ ├──────────┼──────────────────┼┤ │ < OK > <│Cancel > < Help > ││ └──────────┼──────────────────┼┘ │ │ Prints all Prints module in loaded modules active window Figure 11.7 Print Dialog Box 11.11 DOS Shell Command (Full Menus Only) The DOS Shell command on the File menu lets you return temporarily to the DOS command level, where you can execute other programs and DOS commands. QuickBASIC remains in memory so you can return to the same place in your program, without reloading it. QuickBASIC needs to find the COMMAND.COM file before it can execute the Shell command. QuickBASIC looks for COMMAND.COM first in the directory specified in the COMSPEC environment variable, then in the current directory. See your DOS documentation for more information about COMMAND.COM and COMSPEC. Follow these steps to return to QuickBASIC from the DOS command level: 1. Type exit 2. Press ENTER The QuickBASIC screen reappears as you left it. 11.12 Exit Command The Exit command on the File menu removes QuickBASIC from memory and returns you to the DOS prompt. When you exit from a new or modified program that has not been saved, QuickBASIC displays the dialog box shown in Figure 11.8. ┌──────────────────────────────────────────────────────────┐ │ │ │ One or more loaded files are not saved. Save them now? │ │ │ ├──────────────────────────────────────────────────────────┤ │ ┌── < Yes > < No > < Cancel > < Help > ──┐ │ └─────┼────────────────┼──────────┼──────────────────┼─────┘ │ │ │ │ Saves the Returns to DOS Stays in Provides help on file(s) without saving QuickBASIC the dialog box the program environment Figure 11.8 Exit Dialog Box To exit from QuickBASIC after the Exit dialog box has been called up, use one of these procedures: 1. To save the program in its current state and then exit, choose Yes or press ENTER. If this is a new program that you haven't named yet, QuickBASIC displays a dialog box similar to the Save dialog box. See Section 11.4 for more information on this dialog box. 2. To return to DOS without saving the file in its current state, choose No or type N. To stay in the QuickBASIC environment (that is, not exit to DOS after all), press ESC. See Also Section 11.5, "Save As Command"; Section 11.11, "DOS Shell Command" ──────────────────────────────────────────────────────────────────────────── Chapter 12 Using the Editor This chapter describes how to enter and edit program text using QuickBASIC editing commands. Before beginning this chapter, you should be familiar with the QuickBASIC screen and the techniques described in Chapter 10, "Getting Around in QuickBASIC." This chapter includes information on ■ Performing simple editing functions such as entering text and moving the cursor ■ Deleting and inserting text ■ Moving and copying blocks of text ■ Searching for and replacing characters, words, or a group of words ■ Copying text from other files 12.1 Entering Text New characters are added to the text either by inserting or overtyping. In "insert mode," the QuickBASIC editor inserts each new character to the left of the cursor position. In "overtype mode," each new character replaces the character under the cursor. You switch between insert mode and overtype mode by pressing the INS key or CTRL+V. The cursor is a blinking underscore in insert mode and a blinking box in overtype mode. When typing a QuickBASIC program, you can enter a line (tell QuickBASIC that you have completed one or more BASIC statements) either by pressing the ENTER key at the end of the line or by moving the cursor off the line. If the Syntax Checking command is on (Options menu, Full Menus only), QuickBASIC checks the line for proper statement syntax. 12.2 Selecting Text Before you can perform editing functions that manipulate blocks of text (copying and deleting), you must indicate the portion of text you wish to edit by selecting (highlighting) it. Selecting tells both you and the computer which text will be changed by the next command. Hold down the SHIFT key while using the DIRECTION keys or any of the editing shortcut keys (see Section 10.2.2, "Using Shortcut Keys") to select text. For example, press SHIFT+END to select everything from the cursor to the end of a line. To remove highlighting, press any DIRECTION key. ────────────────────────────────────────────────────────────────────────── IMPORTANT If you begin typing while the text is still selected, what you type replaces the selected text. ────────────────────────────────────────────────────────────────────────── 12.3 Indenting text Indent text to improve the readability and structured appearance of your program. Appropriate use of indenting can aid debugging. Use the SPACEBAR or TAB key to indent a single line of text. To indent a block of text, select the lines you wish to indent, then press TAB. Indenting is an integral part of well-structured programs──programs that are highly readable, logical and self-explanatory. QuickBASIC offers several indentation controls, listed in Table 12.1 Table 12.1 QuickBASIC Indentation Controls Keystrokes Description ────────────────────────────────────────────────────────────────────────── (Automatic) Indents each new line automatically, maintaining the current indentation level. HOME Cancels automatic indentation on a blank line and moves cursor to the left margin. BACKSPACE Moves indentation back one level. CTRL+Q+S Moves cursor to the left margin of a line containing indented text. SHIFT+TAB Removes leading spaces for one indentation level. If a block of text is selected, the whole block is moved to the left. ────────────────────────────────────────────────────────────────────────── The default tab setting is eight spaces. You can change the tab setting as follows: 1. Choose the Display command from the Options menu. 2. Select the Tab Stops display option. 3. Enter the new tab-stop setting. 4. Press ENTER. QuickBASIC uses individual spaces (rather than the literal tab character, ASCII 9) to represent indentation levels. The Tab Stops option in the Option menu's Display dialog box sets the number of spaces per indentation level. Some text editors use literal tab characters to represent multiple spaces when storing text files. Refer to Appendix B, "Differences from Previous Versions of BASIC," in Programming in BASIC if you work with files originally created with such an editor or if you suspect that your text editor uses literal tab characters. See Also Section 20.1, "Display Command" 12.4 Using Placemarkers in Text If you are working on different parts of a large program, you can tell QuickBASIC to remember where in the program you are working (set a "place-marker"). This makes it possible to jump between different markers as needed. You can set up to four placemarkers, numbered 0-3, anywhere in your program. Follow these steps to use placemarkers: ■ Put the cursor on the line you want to mark. Press CTRL+K and then n to set placemarker number n. ■ Press CTRL+Q and then n to move to placemarker number n. 12.5 The Smart Editor QuickBASIC Version 4.5 combines a text editor, a compiler, and a debugger into a single "smart editor." The smart editor includes special features that make it easier to enter and edit BASIC programs. When the smart editor is on, QuickBASIC performs the following actions each time you enter a line: ■ Checks the line for syntax errors. ■ Formats the line as needed. ■ Translates the line to executable form, if the syntax is correct. This means that each line you enter is ready to run immediately. 12.5.1 When Is the Smart Editor On? In most cases, you use the QuickBASIC editor to enter and edit program text. If you start QuickBASIC and begin typing, QuickBASIC assumes that you want to write BASIC statements and turns on the smart editor. The smart editor is also on when you do either of the following: ■ Choose New Program or Open Program from the File menu. ■ Choose Create File or Load File from the File menu, then select the Module or Include option in the dialog box. You may occasionally need to edit a text file consisting of something other than BASIC statements, such as a QuickBASIC .MAK file or document file. For this purpose, you can turn off the smart-editor features and use the environment as an ordinary word processor. Do this by choosing Create File or Load File from the File menu, then selecting the Document option in the dialog box. 12.5.2 Automatic Syntax Checking When the smart editor is on, it checks the syntax of each line when it is entered. A syntax error indicates that the line contains a statement that is not meaningful to QuickBASIC. For instance, this line causes a syntax error because the keyword GOTO is not a valid argument for the PRINT statement: PRINT GOTO When an error occurs, QuickBASIC displays an error message. Press ESC or SPACEBAR to clear the message from the screen and position the cursor where the error occurred. You must correct syntax errors before your program will run. ────────────────────────────────────────────────────────────────────────── NOTE When you clear a syntax-error message, the cursor is placed on the statement that caused the error. Press F1 for on-line help with the syntax of the statement. ────────────────────────────────────────────────────────────────────────── Certain typing mistakes are not recognized as syntax errors when entered. For example, no error message appears if you enter the following line instead of the PRINT keyword: pront Although this does not look like a valid BASIC statement, QuickBASIC does not flag the error until you try to run the program. Until then, QuickBASIC interprets the statement as a call to a SUB procedure named pront. Syntax checking is always on unless you choose Create File or Load File commands and choose the Document option. You can toggle syntax checking off and on with the Syntax Checking command from the Options menu. A bullet (■) appears next to the command when syntax checking is toggled on. 12.5.3 Error Messages QuickBASIC translates statements to executable code as they are entered, if there are no syntax errors. If there are syntax errors, QuickBASIC displays a dialog box containing the appropriate error message. If QuickBASIC displays an error message that puzzles you, you can get further information. For more information on the error message, choose the Help command button in the dialog box. To get more information on the use of the statement that caused the error, choose OK in the dialog box and do either of the following steps: ■ Choose the Topic command on the Help menu. ■ Press F1 Often you will see the error message Syntax error, but some error messages are more specific. For example, suppose you enter the following line, which is missing a file name: OPEN, I, 1, QuickBASIC generates the syntax-error message Expected: expression as shown in Figure 12.1: Incomplete statement │ │ File Edit View Search Run Debug Options Help ┌┼─────────────────────────────── Untitled ───────────────────────────┤├── │OPEN,I, 1, │ │ │ │ │ ┌────────────────────────┐ │ │ │ │ ┌────── │ Expected: expression │ ───────┐ │ │ │ │ │ │ │ ├────────────────────────┤ │ │ │ │ < OK > < Help > │ │ │ │ └────────────────────────┘ │ │ │ │ │ │ │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├───────────────┼─────────────── Immediate ───────────────┼───── ────────── │ │ │ │ │ │ <Shift+F1=Help>│<F6=Window> <F2=Subs> <F5=Run> <F8=Step> │ C 00001:005 │ │ Type of syntax error Provides help on the erro Figure 12.1 Syntax Error Message In the case above, do the following to get on-line help on the OPEN statement: 1. Choose OK in the dialog box. 2. Place the cursor in the OPEN keyword. 3. Press F1. The initial on-line help screen is displayed, as shown in Figure 12.2. Different usages of OPEN │ │ File Edit View Search Run Debug Calls Options Help ┌┼───────────── HELP: OPEN (File I/O) Statement QuickSCREEN ──────────┤├── ││ QuickSCREEN Details Example Contents Index │├──────────────────────────────────────────────────────────────────────── │OPEN - a file I/O statement that enables I/O to a file or device ││ │Syntax ││ OPEN file [FOR mode1] [ACCESS access] [lock] AS [#]filenum [LEN=reclen] ││┌─ │││■ file is a string expression that specifies an optional device name, │└┤ followed by a file name or path name │ │■ filenum is an integer expression whose value is between 1 and 255 │ └─ │Other Uses of the OPEN Keyword │ OPEN COM - to open a communications channel │ │See Also GET PUT SEEK INPUT # PRINT # FREEFILE │ ├──────────────────────────────── Untitled ───────────────────────────┤├── │OPEN,I,1,──────┐ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├───────────────┼─────────────── Immediate ──────────────────────────────── │ │ │ │ <Shift+F1=Help>│<F6=Window> <F2=Subs> <F5=Run> <F8=Step> C 00001:003 │ Program text Figure 12.2 Initial Help Screen on the OPEN Keyword In the screen shown in Figure 12.2, choose the usage you are interested in by putting the cursor anywhere on the appropriate line and pressing F1. Notice that your program text remains visible on the screen when you are using on-line help. To exit on-line help, press ESC. See Also Chapter 8, "Statement and Function Summary," and Appendix I, "Error Messages," in Programming in BASIC. 12.5.4 Automatic Formatting In addition to checking for syntax errors, the smart editor automatically standardizes the format of each line as you enter it. The editor makes the following changes: ■ Changes all BASIC keywords to uppercase letters. ■ Inserts spaces before and after all BASIC operators. ■ Keeps capitalization consistent in all references to variables or procedures. ■ Adds punctuation where appropriate. For instance, the smart editor inserts semicolons between consecutive items in a PRINT statement if you do not include them yourself. It also supplies a matching final quotation mark to the argument of a PRINT statement if you forget it. QuickBASIC keeps track of the names of all variables and procedures in your program and capitalizes these names consistently. It changes the capitalization of all occurrences of a variable or procedure name to the reflect the most recently entered version. For example, if you first name a variable MyVar (uppercase M and V), and later enter it as myvar (all lowercase), QuickBASIC changes all instances of MyVar to myvar. 12.6 Entering Special Characters QuickBASIC has procedures for entering the literal representations of special characters, including high-order ASCII characters and the literal ASCII characters associated with control sequences. (In general, entering such literal characters makes your programs more readable but less portable. For portability, use the CHR$ function. See Section 9.5, "Summary of String Processing Statements and Functions," in Programming in BASIC.) High-order ASCII characters are those corresponding to decimal 128-255. You can enter them directly in your QuickBASIC program by holding down the ALT key while you type the appropriate decimal code on the numeric keypad. For example, holding down the ALT key while you enter 205 produces the double-line character at the cursor. Many of the low-order ASCII characters corresponding to decimal 1-27 are associated with both literal characters and special actions. For example, the ASCII character represented by ALT+25 is associated with both the down-arrow character (<143>) and 'Y (command to delete the current line). You may want to enter the down arrow in a PRINT statement. One way to do this is to specify decimal 25 as the argument to the CHR$ function. See Appendix D, "Keyboard Scan Codes and ASCII Character Codes," in Programming in BASIC for decimal equivalents of ASCII characters. However, you can also enter the literal character itself by using the following method: 1. Hold down the CTRL key while pressing the letter P. This produces the 'P character on the QuickBASIC status bar. While this character is displayed, you can enter a CTRL-key sequence to produce its literal character. 2. Hold down the CTRL key again, this time pressing the letter corresponding to the literal character you want. This enters the literal ASCII character (as opposed to the special action of the control sequence) at the cursor. For example, if you want to enter the down-arrow () character within the quotation marks of a PRINT statement, you can enter it as CTRL+P+Y. If you tried to enter it as CTRL+Y or as ALT+25 while 'P was not visible on the reference bar, your line would be deleted. Note that you cannot use this technique for entering the characters corresponding to the following: 'J, 'L, 'M, 'U. See Appendix D, "Keyboard Scan Codes and ASCII Character Codes," in Programming in BASIC for a complete list of the ASCII characters. 12.7 Summary of Editing Commands QuickBASIC's editor is designed to be flexible; it supports a keyboard interface familiar to users of other Microsoft products such as Microsoft Word. Many combinations of the CTRL key with other keys are familiar to users of WordStar and similar editors. Table 12.2 summarizes all the QuickBASIC editing commands. Table 12.2 Editing Commands ╓┌─┌────────────────────────────────────┌──────────────────┌─────────────────╖ WordStar-Style Keypad Keys Key Combinations ────────────────────────────────────────────────────────────────────────── Moving Cursor Character left LEFT CTRL+S Character right RIGHT CTRL+D WordStar-Style Keypad Keys Key Combinations ────────────────────────────────────────────────────────────────────────── Character right RIGHT CTRL+D Word left CTRL+LEFT CTRL+A Word right CTRL+RIGHT CTRL+F Line up UP CTRL+E Line down DOWN CTRL+X First indentation level HOME --- Column 1 of current line --- CTRL+Q+S Beginning of next line CTRL+ENTER CTRL+J End of line END CTRL+Q+D Top of window --- CTRL+Q+E Bottom of file --- CTRL+Q+X Beginning of module/procedure CTRL+HOME CTRL+Q+R End of module/procedure CTRL+END CTRL+Q+C Set marker --- CTRL+K n Move to marker --- CTRL+Q n Inserting Insert mode on or off INS CTRL+V WordStar-Style Keypad Keys Key Combinations ────────────────────────────────────────────────────────────────────────── Insert mode on or off INS CTRL+V Line below END+ENTER --- Line above --- HOME CTRL+N Contents of Clipboard SHIFT+INS --- Tab at cursor or beginning of each TAB CTRL+I selected line Control character at cursorposition --- CTRL+P CTRL+key Deleting Current line, saving in Clipboard --- CTRL+Y To end of line, saving in Clipboard --- CTRL+Q+Y Character left BKSP CTRL+H Character at cursor DEL CTRL+G Word --- CTRL+T Selected text, saving in Clipboard SHIFT+DEL --- Selected text, not saving in DEL CTRL+G Clipboard Leading spaces for one indentation SHIFT+TAB --- WordStar-Style Keypad Keys Key Combinations ────────────────────────────────────────────────────────────────────────── Leading spaces for one indentation SHIFT+TAB --- level of selected lines Copying Save selected text to Clipboard CTRL+INS --- Scrolling Up one line CTRL+UP CTRL+W Down one line CTRL+DOWN CTRL+Z Page up PGUP CTRL+R Page down PGDN CTRL+C Left one window CTRL+PGUP --- Right one window CTRL+PGDN --- Selecting Character left SHIFT+LEFT --- Character right SHIFT+RIGHT --- Current line SHIFT+DOWN --- WordStar-Style Keypad Keys Key Combinations ────────────────────────────────────────────────────────────────────────── Current line SHIFT+DOWN --- Line above SHIFT+UP --- Word left SHIFT+CTRL+LEFT --- Word right SHIFT+CTRL+RIGHT --- Screen up SHIFT+PGUP --- Screen down SHIFT+PGDN --- Screen left SHIFT+CTRL+PGUP --- Screen right SHIFT+CTRL+PGDN --- To beginning of module/procedure SHIFT+CTRL+HOME --- To end of module/procedure SHIFT+CTRL+END --- ────────────────────────────────────────────────────────────────────────── ──────────────────────────────────────────────────────────────────────────── Chapter 13 The Edit Menu The Edit menu controls the functions used to build and manipulate your program code (text). Use the Edit menu to cut, copy, and paste text, to undo your last edit, and to create SUB and FUNCTION procedures. The Edit menu has the following commands: ■ Undo. Reverses your last command or action, restoring the current line to its previous state (Full Menus only). ■ Cut. Deletes selected text and places it on the Clipboard. ■ Copy. Places a copy of selected text on the Clipboard. ■ Paste. Inserts the contents of the Clipboard at the cursor. ■ Clear. Deletes selected text permanently (Full Menus only). ■ New SUB. Creates a new SUB procedure in its own window (Full Menus only). ■ New FUNCTION. Creates a new FUNCTION procedure in its own window (Full Menus only). 13.1 Understanding the Clipboard The editor in QuickBASIC uses a Clipboard, which is the part of your computer's memory used to temporarily store blocks of text you have cut or copied. If you have used a word processor to cut, copy, and paste text, you are familiar with the Clipboard concept. When you use the Cut or Copy command to move, remove, or duplicate a section of text, that text is stored in the Clipboard. You can then use the Paste command to insert the Clipboard's contents as many times as you like; Paste does not alter the contents of the Clipboard. But any time you use the Cut or Copy command, the contents of the Clipboard are replaced by new contents. 13.2 Undo Command (Full Menus Only) The Undo command on the Edit menu reverses any changes made to the current line. Once the cursor moves off the line, however, Undo cannot restore the line to its previous state. Undo works on the current line immediately after you make changes to it. Choosing Undo on an unaltered line has no effect. ────────────────────────────────────────────────────────────────────────── NOTE Undo cannot restore text deleted with CTRL+Y, which removes an entire line. However, a copy of the line is placed on the Clipboard, so you can restore it with the Paste command. ────────────────────────────────────────────────────────────────────────── Shortcut Key ALT+BKSP 13.3 Cut Command The Cut command removes selected text from the screen and places it on the Clipboard. When no text is selected, the Cut command is not available. Use Cut and Paste together to relocate lines or blocks of text as follows: 1. Select the text you wish to move (it may be as many lines as you wish). 2. Choose the Cut command from the Edit menu. 3. Move the cursor to the point where you wish to insert the text. 4. Choose the Paste command from the Edit menu. You can use this sequence to move entire blocks of a program from one section to another, reducing the time it takes you to write new programs. ────────────────────────────────────────────────────────────────────────── NOTE The Clipboard contains only the most recently cut or copied text. ────────────────────────────────────────────────────────────────────────── Shortcut Key SHIFT+DEL See Also Section 13.4, "Copy Command"; Section 13.5, "Paste Command"; Section 13.6, "Clear Command" 13.4 Copy Command The Copy command places a copy of selected text on the Clipboard, leaving the original text unchanged. Copying replaces any previous contents on the Clipboard. Use the Copy and Paste commands together to duplicate sections or lines of program code. For example, you can use the following sequence to speed the creation of similar SUB procedures: 1. Select the text you wish to duplicate (it may be as many lines as you wish). 2. Choose the Copy command from the Edit menu. 3. Move the cursor to the point at which you wish to insert the text. 4. Choose the Paste command from the Edit menu. 5. Customize the copied text for a new line, procedure or section of program text. ────────────────────────────────────────────────────────────────────────── NOTE The Clipboard contains only the most recently cut or copied text. ────────────────────────────────────────────────────────────────────────── Shortcut Key CTRL+INS See Also Section 13.3, "Cut Command"; Section 13.5, "Paste Command" 13.5 Paste Command The Paste command inserts a copy of the Clipboard's contents to the right of the cursor. Paste works only when the Clipboard contains text. If you have text selected, the Paste command replaces the selected text with the contents of the Clipboard. If no text is selected, Paste inserts the contents of the Clipboard to the right of the cursor, or above the cursor if the Clipboard contents exceed one line. Shortcut Key SHIFT+INS See Also Section 13.3, "Cut Command"; Section 13.4, "Copy Command" 13.6 Clear Command (Full Menus Only) The Clear command completely removes selected text from your file. Cleared text is not transferred onto the Clipboard and cannot be replaced by using the Paste command. Pressing the DEL key without text selected removes the character to the right of the cursor. ────────────────────────────────────────────────────────────────────────── WARNING Use the Clear command with care; you can restore cleared text only by using the Undo command immediately. ────────────────────────────────────────────────────────────────────────── Shortcut Key DEL See Also Section 13.2, "Undo Command"; Section 13.3, "Cut Command" 13.7 New SUB Command (Full Menus Only) The Edit menu's New SUB command creates and names a new SUB procedure as part of the module in the active window. The next time you save your program, all new procedures are added to the program's module. SUB procedures can be defined in the main module or other modules, and can be moved from one module to another by using the SUBs command from the View menu. Use SUB procedures for repetitive operations, including ones which manipulate information (arguments) you give the SUB. For example, you might define a SUB procedure CenterText, which centers text on the screen. If you enter the following line in your program: CALL CenterText("Hourly wage") the phrase Hourly wage appears in the center of your screen (the actual SUB code is omitted here). ────────────────────────────────────────────────────────────────────────── IMPORTANT A procedure name can appear only once in a program. An error occurs if the same name appears more than once. ────────────────────────────────────────────────────────────────────────── See Also Chapter 5, "The QCARDS Program," in this manual; Chapter 2, "SUB and FUNCTION Procedures," in Programming in BASIC. 13.7.1 Creating a New SUB Procedure Create a new SUB procedure by following these steps: 1. Choose New SUB from the Edit menu. A dialog box appears. 2. Type the name for the new SUB procedure in the text box, as shown in Figure 13.1. New SUB name │ ┌─────────┼── New SUB ─────────────┐ │ ┌─┼──────────────────────┐ │ │ Name: │Initvar │ │ │ └────────────────────────┘ │ │ │ ├──────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └──────────────────────────────────┘ Figure 13.1 New SUB Dialog Box 3. Press ENTER. The New SUB command opens a new window with the SUB and END SUB statements already in place, ready for you to enter the procedure. When you complete the procedure, use the SUBs command from the View menu to return to the module-level code, another procedure, or another module. Note that if you type SUB subname, QuickBASIC starts the procedure immediately, bypassing the need to open the menu or dialog box. When you start a new "procedure" (the collective term for SUB and FUNCTION procedures) either by typing SUB or FUNCTION followed by the procedure name or by using the New SUB or New FUNCTION command from the Edit Menu, QuickBASIC displays the procedure in the View window. 13.7.2 Default Data Types for Procedures Data type, determined by a DEFtype statement, refers to the type of data a particular range of names will have. The DEFtype statement is a generic term that collectively refers to the data definition statements DEFINT (define integer), DEFSNG (define single precision), DEFDBL (define double precision), DEFLNG (define long integer), and DEFSTR (define string). A range of letters follows the DEFtype statement, indicating the range of names affected by the DEFtype statement. For example, DEFDBL M-Q defines all variables with names beginning with letters in the range M-Q to be double precision. In a new procedure, QuickBASIC automatically inserts a DEFtype statement at the top of the View window, ahead of the line containing the SUB keyword: DEFtype letter1-letter2 SUB SubName END SUB or DEFtype letter1-letter2 FUNCTION FunctionName END FUNCTION In the preceding example, letter1 and letter2 indicate the letter range the DEFtype statement affects. Note that you may omit letter2 if you want to define only a single letter as a specific data type. Which DEFtype is automatically added to the procedure depends on whether there are DEFtype statements at the module level. If there are no DEFtype statements in the main module, QuickBASIC creates the procedure without a DEFtype statement, and the new procedure defaults all variables to single precision. If there are one or more DEFtype statements at the module level, QuickBASIC includes all DEFtype statements other than DEFSNG in the new procedure. Any variable that falls outside of the letter range indicated by any of the other DEFtype statements defaults to single precision. 13.7.3 Changing a Procedure's Default Type If QuickBASIC inserts a DEFtype statement you do not want, you can remove it (in which case the default for that procedure becomes single precision), or you can change it by overtyping. When you have no DEFtype statements in your main module, QuickBASIC omits the DEFtype statement in new procedures (and procedure variables default to single precision). You can add new DEFtype statements to the procedure by placing them in front of the SUB or FUNCTION statement (in insert mode) and pressing ENTER. 13.7.4 Saving and Naming Procedures When you save a program, QuickBASIC creates a declaration for each procedure at the beginning of the module containing the procedure. A declaration consists of the DECLARE keyword, followed by the SUB or FUNCTION keyword, then the name of the procedure, and a list of its formal parameters. Procedures are not saved as independent files the way modules are. Therefore procedure names are governed by the naming conventions of QuickBASIC rather than DOS. They are saved within the module in which they are created, or to which they are moved. The rules for naming procedures are the same as those for naming variables. Procedure names can be any valid BASIC name up to 40 characters long. They must be unique. If you give a procedure the same name as a variable, the error message Duplicate definition appears. See Also Section 13.8, "New FUNCTION Command"; Section 14.1, "SUBs Command" 13.8 New FUNCTION Command (Full Menus Only) The New FUNCTION command defines (creates and names) a new FUNCTION procedure as a part of the module or program in the active window. When you save the module, any new procedures become part of that module. Create your own FUNCTION procedures whenever you repeatedly calculate similar quantities. For example, you might define a FUNCTION procedure Volume (X) that calculates the volume of a sphere of radius X. Your program then finds the volume of a sphere of any radius very easily: SphereVol = Volume (rad) ' find volume of a sphere of ' radius rad QuickBASIC sets the value of X equal to rad when it calculates the volume of the sphere. If you need to calculate the volume of a sphere several times, such a FUNCTION procedure could save you space, time, and debugging efforts. ────────────────────────────────────────────────────────────────────────── IMPORTANT A procedure name can appear only once in a program. An error occurs if the same name appears more than once. ────────────────────────────────────────────────────────────────────────── You can define a new FUNCTION procedure by following these steps: 1. Choose New FUNCTION from the Edit menu. A dialog box appears. 2. Type the name for the new FUNCTION procedure in the text box. See Figure 13.2. New FUNCTION name │ ┌─────────┼ New FUNCTION ──────────┐ │ ┌─┼──────────────────────┐ │ │ Name: │Cube │ │ │ └────────────────────────┘ │ │ │ ├──────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └──────────────────────────────────┘ Figure 13.2 New FUNCTION Dialog Box 3. Press ENTER. QuickBASIC opens a new window with the FUNCTION and END FUNCTION statements already in place. When you complete the FUNCTION procedure, use the SUBs command from the View menu to return to the previous module. Keyboard Shortcut Type FUNCTION followed by the name of the new procedure to perform steps 1-3 in the previous list automatically. See Also Chapter 5, "The QCARDS Program"; Section 13.7.2, "Default Data Types for Procedures"; Section 13.7.3, "Changing a Procedure's Default Type"; Section 13.7.4, "Saving and Naming Procedures"; Section 14.1, "SUBs Command." Also see Chapter 2, "SUB and FUNCTIONS Procedures," in Programming in BASIC." ──────────────────────────────────────────────────────────────────────────── Chapter 14 The View Menu The View menu gives the available options for viewing program components. You also use the View menu to move SUB and FUNCTION procedures, modules, include files, and document files in and out of the View window for viewing and editing. The View menu includes the following commands: ■ SUBs. Moves procedures, modules, include files, and document files into and out of windows and moves procedures among modules. ■ Next SUB. Places the next procedure (alphabetical by name) in the active window (Full Menus only). ■ Split. Divides the View window horizontally (Full Menus only). ■ Next Statement. Moves the cursor to the next statement to be executed (Full Menus only). ■ Output Screen. Toggles the screen display between the program output and the QuickBASIC editor. ■ Included File. Loads referenced include files for viewing and editing (Full Menus only). ■ Included Lines. Displays the contents of referenced include files for viewing only. 14.1 SUBs Command The SUBs command lets you select among the currently loaded files, their procedures (SUB and FUNCTION), include files, and document files. When you choose a file or procedure, QuickBASIC displays it in the View window. The SUBs dialog box controls file and procedure handling. To use the SUBs command, follow these steps: 1. Choose the SUBs command from the View menu. The SUBs dialog box appears, as shown in Figure 14.1. Procedures are indented Modules are listed Retains active wi beneath their modules in uppercase letters and places select │ │ item in new windo │ │ │ ┌┼──────────────────────────────┼── SUBs ─────────────────┼───────────── ││ │ │ ││Choose program item to edit │ │ ││┌─────────────────────────────┼─────────────────────────┼───────────── │││ DEMO1.BAS ──────┤ │ │││ DEMO2.BAS ──────────────────┤ │ │││ ┌Bounce │ │ │└┼──┤Fall │ │ │ │ │Klaxon │ │ │ │ └Siren │ │ │ │ TEST.BAS ───────────────────┘ │ │ │ │ │ │ │ │ └▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒ │┌DEMO1.BAS is the Main Module │ ││ │ ││ < Edit in Active > < Edit in Split > ───────┘ < Cancel > ├┼────────────────────────────────────────────────────────────────────── ││ < Delete >──┐ < Move > ┌──< Help > └┼────────────────┼──────────────────────┼──────────────────┼─────────── │ │ │ │ Describes Unloads a module Places procedure Moves procedur item in from memory or in active window from one modul highlighted box Figure 14.1 New SUBs Dialog Box 2. Highlight the module, procedure, or include file you want to work with by pressing the DIRECTION keys. Then you can do one of the following: ■ Choose the Edit in Active button to place your selection in the active window. ■ Choose the Edit in Split button to split the window horizontally; the lower (active) window displays the new selection and the upper window contains the contents of the previous window. Use F6 to cycle down through the windows or SHIFT+F6 to cycle up. To close the extra window choose the Split command from the View menu again. ■ Choose the Move button to move the selected procedure to a different module. A dialog box appears with a list of destination modules. See Figure 14.2. (Moving a procedure in a single-module program has no effect.) Current destination module │ ┌┼─────────────────────────────────┐ ││ Choose destination module: │ ││ ┌────────────────────────────┐ │ ││ │ DEMO1.BAS │ │└─┼ TORUS.BAS ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ │ │ └────────────────────────────┘ │ │ │ ├──────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └──────────────────────────────────┘ Figure 14.2 Move Dialog Box ■ Choose the Delete button to remove the selected procedure completely from the module. (Note that deleting a module removes that module and all of its associated procedures from memory but keeps the module on disk.) ■ Choose Cancel to return to the previous active window. ■ Choose Help for more information on using the SUBs dialog box. You are now ready to work with the module, procedure, or include file you selected. Shortcut Key F2 See Also Section 11.9, "Unload File Command"; Section 14.2, "Next SUB Command"; Section 16.7, "Set Main Module Command" 14.2 Next SUB Command (Full Menus Only) The Next SUB command displays the contents of the next procedure (alphabetically by name) in the active window. If the current module contains no procedures, choosing Next SUB has no effect. You may cycle either forward to the next procedure of backward to the previous one. Next SUB is of particular value when working with modules that contain only a few procedures. For programs with many procedures, the SUBs command is generally faster for moving between program parts. Shortcut Keys SHIFT+F2 (forward) and CTRL+F2 (backward) See Also Section 14.1, "SUBs Command" 14.3 Split Command (Full Menus Only) The Split command divides the View window horizontally, allowing you to work with two parts of a program simultaneously. To use the Split command follow these steps: 1. Choose Split from the View menu. 2. Press F6 to cycle down through the windows, making the different windows active, or SHIFT+F6 to cycle up through the windows. 3. Choose Split again to fill the screen with the active window and close the inactive window. You can increase or decrease the size of a window or expand it to fill the entire screen. To change the size of a window, make it the active window and use the following key combinations (use the PLUS and MINUS keys on the numeric keypad): Key Combination Result ────────────────────────────────────────────────────────────────────────── ALT+PLUS (+) Expands the active window one line. ALT+MINUS (-) Shrinks the active window one line. CTRL+F10 Expands the active window to fill the screen. If it already fills the screen, the window is returned to its former size. ────────────────────────────────────────────────────────────────────────── See Also Chapter 10, "Getting Around in QuickBASIC"; Section 14.1, "SUBs Command" 14.4 Next Statement Command (Full Menus Only) The Next Statement command places the cursor at the next statement to be executed but does not execute the statement. The Next Statement command is typically used after pausing a program for debugging purposes; it allows you to see which statement the Continue command will execute first when you choose it. Next Statement is useful after moving around in a suspended program to return to the original point of suspension. See Also Section 15.1, "Find Command"; Section 16.3, "Continue Command"; Chapter 18, "The Debug Menu" 14.5 Output Screen Command The Output Screen command causes QuickBASIC to switch between the environment and output screens created by your program. This command is functional at any time during editing, but is most useful after the program sends data to the screen. For example, when you run a program that has screen output, QuickBASIC prints the message Press any key to continue on the bottom of the output screen when the program ends. After returning to the QuickBASIC editor, you can switch back and forth between the editor and output screens by choosing the Output Screen command. This allows you to refer to previous output while editing or debugging your program. Shortcut Key F4 14.6 Included File Command (Full Menus Only) The Included File command loads a file referenced with the $INCLUDE metacommand for viewing and editing. When the cursor is on a $INCLUDE metacommand line, choosing the Included File command loads the text of the include file into the active window for editing. QuickBASIC keeps the text of include files separate from the rest of the program text. This is similar to the way in which the text of SUB or FUNCTION procedures is separated from other program text. However, QuickBASIC considers an include file separate from the rest of the program. You may wish to edit an include file without moving the cursor from the line in your program containing the $INCLUDE metacommand. To do so, follow these steps: 1. Split the screen with the Split command from the View menu. 2. Choose the Load File command from the File menu to load the include file. Be sure to select the Include option. 3. Edit the include file. 4. Choose Save from the File menu to save any changes made to the include file. 5. Press F6 to move back to the program in the other View window. 6. Choose the View menu's Split command again to close the extra window. Save the include file to incorporate your changes. QuickBASIC prompts you if you forget. 14.6.1 Nesting Include Files You can have any number of $INCLUDE metacommands in a program. However, the "nesting" of include files is limited. Nesting occurs when a $INCLUDE metacommand appears within another include file. Include files can be nested up to five levels. If you have a circular reference in an include file (that is, a $INCLUDE metacommand that references itself or a file in which it is referenced), you get the error message Too many files when you try to run your program. 14.6.2 Finding Include Files When QuickBASIC processes a $INCLUDE metacommand, it searches first for the include file in any directory specified in the metacommand, then the working directory, and finally any include-file directory indicated by the Set Paths command. If you refer to a directory in the $INCLUDE metacommand itself, you need to include a full or relative path name. For example, the following directs QuickBASIC to look for the include file named declares.bi in the directory c:include: ' $INCLUDE: 'C:includedeclares.bi' This could also be specified with a relative path, as in the following line: ' $INCLUDE: '..includedeclares.bi' Although any extension, including .BAS, is legal for files incorporated into your program with the $INCLUDE metacommand, it is recommended that include files use some unique extension (such as .BI) to avoid confusion with program modules. See Also Section 14.7, "Included Lines Command"; Section 20.2, "Set Paths Command" 14.7 Included Lines Command The Included Lines command lets you view, but not edit, the contents of referenced include files. This command is a toggle; a bullet (■) appears next to the option when it is on. Choosing it again turns it off. The Included Lines command lets you look at the include file's contents, which appear in high-intensity video beneath the appropriate $INCLUDE metacommand. Although you can scroll around in the include file after choosing Included Lines, you cannot edit the include file as long as this option is on. If you try to edit the include file while Included Lines is on, a dialog box appears and asks if you want to edit the include file. If you do, QuickBASIC loads the file into memory and places its text in the active View window. If you try to edit the program file while the Included Lines command is on, a dialog box appears asking if you want to turn the Included Lines command off. If you press ENTER, the include file disappears, and you can then edit the source file in the usual way. For editing files referenced with the $INCLUDE metacommand, use the Included File command or the Load File command on the File menu (remember to choose the Include option). See Also Section 14.6, "Included File Command" ──────────────────────────────────────────────────────────────────────────── Chapter 15 The Search Menu The Search menu lets you find specific text──"target" text──anywhere in a program, and replaces it with new text. The Search menu has several uses, particularly in long or complex programs. For instance, to move quickly to a distant part of your program, you can search for a line label or other identifying text you know to be in that section. The Search menu has the following commands: ■ Find. Searches for and locates the nearest occurrence of designated text. ■ Selected Text. Searches for text that matches the currently highlighted text (Full Menus only). ■ Repeat Last Find. Locates the next occurrence of the text specified in the previous search (Full Menus only). ■ Change. Searches for and then replaces target text with new text. ■ Label. Searches for a specified line label (Full Menus only). 15.1 Defining Target Text Search procedures require you to specify your target text──the text you want to search for. QuickBASIC uses several methods to specify target text. The word containing the cursor or closest to the left of the cursor becomes the default target text. If the cursor is on a blank line, the target text from the previous search becomes the default. You can alter default target text by typing new text in the Find or Change dialog boxes. All searches begin at the cursor and move forward. If QuickBASIC reaches the end of the active window without finding a match, it returns to the top of the document and continues the search until it either locates the text or reaches the original cursor location. You can also select options that extend the search to the entire current module or all modules loaded. 15.2 Find Command The Find command searches for and places the cursor on specified text. The text may consist of a single character, a word, or any combination of words and characters. Enter the text you want to find in the text box of the Find dialog box, shown in Figure 15.1. Text to find │ ┌──────────────┼────────────── Find ────────────────────────────┐ │ ┌─┼────────────────────────────────────────────┐ │ │ Find What: │sum │ │ │ └──────────────────────────────────────────────┘ │ │ │ │ ┌ ┌─────────────────────────┐ │ │┌┤[ ] Match Upper/Lowercase │ ( ) 1. Active Window ─┐ │ │ │││[ ] Whole Word │ (∙) 2. Current Module ├─┼─┐ │ ││└ │ ( ) 3. All Modules ─┘ │ │ │ ││ └─────────────────────────┘ │ │ ├┼────────────────────────────────────────────────────────────┼─┤ ││ < OK > < Cancel > < Help > │ │ └┼────────────────────────────────────────────────────────────┼─┘ │ │ Search restrictions Search options Figure 15.1 Find Dialog Box The dialog box also controls the extent of the search (whether the search includes the active window, the current module, or all files currently loaded in QuickBASIC) and any restrictions on the search. To perform a search, do the following: 1. Choose Find from the Search menu. A dialog box appears. 2. Enter the text you want to find in the Find What text box. (Any default target text appears highlighted.) 3. Select any search option buttons by pressing the TAB and DIRECTION keys. (See Table 15.1 for a list of available options.) 4. Set any restrictions by pressing the TAB key to select the option and SPACEBAR to turn the option on or off. (See Table 15.2 for a list of restrictions.) 5. Press ENTER to begin the search. If it cannot locate the target text, QuickBASIC displays the message Match not found and leaves the cursor where it was when you started the search. Press ENTER or ESC to remove the message and continue. The options available with search commands are listed in the following table: Table 15.1 Search Options Option Description ────────────────────────────────────────────────────────────────────────── Active Window Searches only in the current, active window Current Module Searches only in the current module (including procedures) All Modules Searches all parts of all loaded files ────────────────────────────────────────────────────────────────────────── The following table lists the restrictions you can set with the Find command: Table 15.2 Search Restrictions Restriction Description ────────────────────────────────────────────────────────────────────────── Match Upper/Lowercase Searches for text that matches exactly. For example, if CHR is the specified text, the Match Upper/Lowercase option finds CHR but not Chr. Whole Word Locates the target as a separate word. Whole words include words surrounded by spaces, punctuation marks, or other characters not considered parts of words. Word parts include A$MIZ, a$MIz, 0$MI9, and !, #, $, %, and & (commonly used in declarations). For example, a whole word search for CHR would locate CHR: but not CHR$ or CHARACTER. ────────────────────────────────────────────────────────────────────────── See Also Section 15.5, "Change Command" 15.3 Selected Text Command (Full Menus Only) The Selected Text command on the Search menu searches for text that matches text selected in the active window. Follow these steps to use the Selected Text command: 1. Select the text you want to find. The text must fit on one line (256 characters). 2. Choose the Selected Text command from the Search Menu. QuickBASIC highlights the next occurrence of the selected text and puts the cursor at the first character of the string. If there are no other occurrences, the screen remains the same. Shortcut Key CTRL +<FS> See Also Section 15.2, "Find Command" 15.4 Repeat Last Find Command (Full Menus Only) The Repeat Last Find command searches for the next occurrence of the text specified in the last search. Text specified in the previous Find or Change command becomes the target text of a Repeat Last Find search. If you have not used the Find or Change commands and you choose the Repeat Last Find command, QuickBASIC uses the word containing the cursor, or the word nearest to the left of the cursor, as the default target text. Shortcut Key F3 See Also Section 15.2, "Find Command" 15.5 Change Command The Change command searches for one text string and replaces it with another. Either string may consist of a single character, a single word, or any combination of words and characters. Use the Change dialog box, shown in Figure 15.2, to enter the target text, the replacement text, and search attributes and restrictions. Text to change Replacement text │ │ ┌──────────────────┼───┼───── Change ───────────────────────────┐ │ ┌─────┼───┼────────────────────────────────────┐ │ │ Find What: │sum ─┘ │ │ │ │ └─────────┼────────────────────────────────────┘ │ │ ┌─────────┼────────────────────────────────────┐ │ │ Change To: │total ───┘ │ │ │ └──────────────────────────────────────────────┘ │ │ │ │ ┌ ┌─────────────────────────┐ │ │┌┤[ ] Match Upper/Lowercase │ ( ) 1. Active Window ─┐ │ │ │││[ ] Whole Word │ (∙) 2. Current Module ├─┼─┐ │ ││└ │ ( ) 3. All Modules ─┘ │ │ │ ││ └─────────────────────────┘ │ │ ├┼────────────────────────────────────────────────────────────┼─┤ ││ < Find and Verify > < Change All > < Cancel > < Help > │ │ └┼────────────────────────────────────────────────────────────┼─┘ │ │ Search restrictions Search options Figure 15.2 Change Dialog Box To change text, do the following: 1. Choose Change from the Search menu. 2. Type the text you want to replace in the Find What text box. 3. Type the replacement text in the Change To text box. 4. Select any search options you desire (see Table 15.1). 5. Set any search restrictions (see Table 15.2). 6. Choose Find and Verify or Change All to begin replacing text, or Cancel to cancel the command. ■ Find and Verify finds the target text, then displays four more buttons: Change, Skip, Cancel, and Help. Change executes the change, Skip searches for the next occurrence (without making any changes), and Cancel stops the search and returns to the point at which the search began. Help provides more information about the Find and Verify dialog box. See Figure 15.3. Stops search and Executes the change returns to active window │ │ ┌────────┼──────────────────────┼───────────────────┐ │ │ │ │ ├────────┼──────────────────────┼───────────────────┤ │ < Change > < Skip > < Cancel > < Help > │ └────────────────────┼───────────────────────┼──────┘ │ │ Searches for Provides help on change next occurrence Figure 15.3 Change, Skip, Cancel Dialog Box ■ Change All finds and replaces all occurrences of the target text without asking for confirmation. ■ Cancel returns control to the active window. ■ If it cannot locate the target text, QuickBASIC displays the message Match not found Press ENTER to remove the message and continue. ────────────────────────────────────────────────────────────────────────── IMPORTANT The Undo command on the Edit menu cannot undo a change made with the Change command. Use particular caution with Change All since this command can drastically alter your program. ────────────────────────────────────────────────────────────────────────── See Also Section 15.2, "Find Command" 15.6 Label Command (Full Menus Only) The Label command searches for a line label. Since line labels require a colon, QuickBASIC searches for your text-box entry plus a colon. QuickBASIC searches only for the target text followed by a colon. For example, if you enter mylab as your target text in the Label dialog box, QuickBASIC searches for mylab: The Label dialog box is shown in Figure 15.4. Name of label │ ┌────────────────────┼────── Label ─────────────────────────────┐ │ ┌───────┼──────────────────────────────────────┐ │ │ Find What: │MyLab ─┘ │ │ │ └──────────────────────────────────────────────┘ │ │ │ │ ┌ ┌─────────────────────────┐ │ │┌┤[ ] Match Upper/Lowercase │ ( ) 1. Active Window ─┐ │ │ │││[X] Whole Word │ (∙) 2. Current Module ├─┼─┐ │ ││└ │ ( ) 3. All Modules ─┘ │ │ │ ││ └─────────────────────────┘ │ │ ├┼────────────────────────────────────────────────────────────┼─┤ ││ < OK > < Cancel > < Help > │ │ └┼────────────────────────────────────────────────────────────┼─┘ │ │ Search restrictions Search options Figure 15.4 Label Dialog Box See Also Section 15.2, "Find Command"; Section 15.3, "Selected Text Command" ──────────────────────────────────────────────────────────────────────────── Chapter 16 The Run Menu The Run menu contains commands that let you control program execution within QuickBASIC, compile stand-alone programs with the BC compiler, and create Quick libraries. This allows you to create and debug your program within QuickBASIC, then compile your running program for greater speed. As stand-alone applications, your programs can be run from the DOS command line──without being loaded into QuickBASIC. You also use the Run menu to define main program modules. The Run menu has the following commands: ■ Start. Runs the currently loaded program from within the QuickBASIC environment. ■ Restart. Resets all variables to zero and all string expressions to zero-length strings, and prepares to execute the first statement in the program. ■ Continue. Resumes execution of a suspended program at the statement where execution was stopped (does not reset variables or expressions). ■ Modify COMMAND$. Accesses the string passed to a program via the COMMAND$ function from the DOS command line (Full Menus only). ■ Make EXE File. Creates an executable file from the currently loaded program. ■ Make Library. Creates a custom Quick library (Full Menus only). ■ Set Main Module. Sets a selected module as the main module (Full Menus only). 16.1 Start Command The Start command on the Run menu runs the currently loaded program. Once you start a program you may stop it by pressing CTRL+BREAK. To continue running the program from where you stopped, choose the Continue command from the Run menu. To start from the beginning again, choose Start. ────────────────────────────────────────────────────────────────────────── NOTE If you load a BASICA program, some statements require modification to run properly with QuickBASIC. They are described in Appendix A,"Converting BASICA Programs to QuickBASIC," in Programming in BASIC. ────────────────────────────────────────────────────────────────────────── Shortcut Key SHIFT+F5 See Also Section 16.2, "Restart Command"; Section16.3, "Continue Command"; Section 16.5, "Make EXE File Command" 16.2 Restart Command The Restart command on the Run menu resets all variables to zero and all string expressions to zero-length strings. It prepares your program to run, but does not begin execution. Restart also highlights the first executable statement in your program. Restart is generally used during debugging when you do not want to continue execution. It is especially useful if you want to restart a program from the beginning and step through program code (using the F8 key) prior to the first breakpoint or watchpoint. (Breakpoints and watchpoints are devices used to halt program execution. See Section 18.3, "Watchpoint Command," and Section 18.8, "Toggle Breakpoint Command.") If you want to execute to the first breakpoint or watchpoint without stepping through code, use the Start command. To run your program from a specific location without resetting any variables or expressions, use the Continue command on the Run menu or the Set Next Statement command on the Debug menu followed by the Continue command. See Also Section 16.1, "Start Command"; Section 16.3, "Continue Command"; Section 18.11, "Set Next Statement Command" 16.3 Continue Command The Continue command continues an interrupted program from the last statement executed or starts a program from the beginning. The Continue command is particularly useful for debugging. Use Continue to run a program from one breakpoint or watchpoint to another. When execution stops, you can analyze the code and make any corrections. Once you complete the corrections, choose Continue to execute from that point forward. If you make a change that prevents continuation from the current statement, QuickBASIC stops and asks if you want to continue without the change or if you prefer to include the change and restart the program. (If you do not want to restart, you can frequently use the Immediate window to make temporary changes that will allow the program to continue.) Shortcut Key F5 See Also Section 16.1, "Start Command"; Section 16.2, "Restart Command" 16.4 Modify COMMAND$ Command (Full Menus Only) The Modify COMMAND$ command is a feature helpful to advanced programmers who want to access text strings passed to their programs from the DOS command line via the COMMAND$ function. You only need the Modify COMMAND$ command if your program uses the COMMAND$ function. In some applications, you may wish to pass information from the DOS environment to the application. For example, typing QB DEMO1 lets QuickBASIC know that you wish to work within the program DEMO1 in the QuickBASIC environment. DEMO1 is information that is passed to QuickBASIC from the command line. You can pass information to your program from the DOS command-line using the COMMAND$ function. Memory is cleared every time the program starts, and the information from the DOS command line is lost. In the development and debugging process, you will want to test the program without exiting to DOS each time you alter the program. The Modify COMMAND$ command tells QuickBASIC to substitute what you have entered in the dialog box for the string the COMMAND$ function would normally return. In the Modify COMMAND$ dialog box, you indicate the string to be returned by the COMMAND$ function. See Figure 16.1. ┌───────────────────── Modify COMMAND$ ─────────────────────┐ │ │ │ Enter text for COMMAND$: │ │ │ │ ┌───────────────────────────────────────────────────┐ │ │┌─ │SAMPLE.EXE WHITE GREEN BLUE │ │ ││ └───────────────────────────────────────────────────┘ │ ├┼──────────────────────────────────────────────────────────┤ ││ < OK > < Cancel > < Help > │ └┼──────────────────────────────────────────────────────────┘ │ Text the COMMAND$ function will return Figure 16.1 Modify COMMAND$ Dialog Box 16.5 Make EXE File Command Once your program runs within QuickBASIC, you can use the Make EXE File command to make a version of the program that runs directly from the DOS command line without being loaded into QuickBASIC. The file for such a program is known as an executable file, and has the extension .EXE. Entering the base name (name with no extension) of an executable file after the DOS prompt runs the program. When you create an executable file, QuickBASIC first uses the BASIC command-line compiler (BC) to compile your BASIC source code into an intermediate file (an object file). QuickBASIC then uses a program called the Microsoft Overlay Linker (LINK) to join all the separately compiled modules of your program into a single executable file. LINK also combines the compiled object files created by BC with the supporting routines your program needs to execute properly. These routines are found in the run-time libraries BRUN45.LIB or BCOM45.LIB. 16.5.1 Creating Executable Files The files in the following list must be available to QuickBASIC when you create an executable file. Make sure they are in the current directory or available through your PATH or LIB environment variables. You can also use the Options menu's Set Paths command to tell QuickBASIC where to search for these files. (See Section 20.2, "Set Paths Command," for more information on setting environment variables.) ╓┌─┌────────────────────────┌────────────────────────────────────────────────╖ Program Purpose ────────────────────────────────────────────────────────────────────────── BC.EXE Creates linkable object files (files with .OBJ extensions) from your program. LINK.EXE Links the object files created by BC. BRUN45.LIB Provides supporting routines that allow your (Full Menus only) BASIC program to perform tasks such as accepting input or printing text on the screen. These routines are linked with your program by Program Purpose ────────────────────────────────────────────────────────────────────────── routines are linked with your program by LINK.EXE. The BRUN45.LIB library is the run-time-module library. Programs linked with this library have small executable files, but can only run in combination with BRUN45.EXE, the run-time module. BCOM45.LIB Provides supporting routines like BRUN45.LIB, except that executable files created with this library do not require BRUN45.EXE (run-time module) support. Files created with BCOM45.LIB are larger than those that use BRUN45.EXE, but will run as stand-alone programs. ────────────────────────────────────────────────────────────────────────── Take the following steps to create an executable file from a program loaded in QuickBASIC: 1. Choose the Make EXE File command from the Run menu. The Make EXE File dialog box appears. See Figure 16.2. Name for executable file │ ┌──────────────────────┼────── Make EXE File ─────────────────────────── │ ┌─────┼──────────────────────────────────────────────── │ EXE File Name: │DEMO1.EXE │ └────────────────────────────────────────────────────── │ │ ┌─[X] Produce Debug Code Produce: │ │ ┌──(∙) EXE Requiring BRUN45.EXE │ │ ├──( ) Stand-Alone EXE File ├─┼─────────────────────────────────┼─────────────────────────────────── │ │ < Make EXE > < Make EXE and│Exit > < Cancel > < Help > └─┼─────────────────────────────────┼─────────────────────────────────── │ │ Provides additional debugging Executable-file options information when checked Figure 16.2 Make EXE File Dialog Box 2. Type a different base name in the text box if you want to rename your file; otherwise, leave the text box alone. 3. Choose either the EXE Requiring BRUN45.EXE option or the Stand-Alone EXE File option. See Section 16.5.3, "Types of Executable Files," for a discussion of these alternatives. 4. Choose Produce Debug Code if you want your executable file to include additional error-checking and to report error locations at run time. Also choose Produce Debug Code if you want your program to respond to CTRL+BREAK. Note that Produce Debug Code does not produce CodeView(R)-compatible files and results in larger and slower programs. See Section 16.5.4, "Run-Time Error Checking in Executable Files," for an explanation of errors handled by this option. 5. Choose either the Make EXE or the Make EXE and EXIT command button: ■ The Make EXE command button creates the executable file, and then returns you to QuickBASIC. ■ The Make EXE and Exit command button creates the executable file, and then returns you to the DOS prompt. 16.5.2 Quick Libraries and Executable Files If your program uses routines from a Quick library, you must load the Quick library when you load your program. If a Quick library is loaded when you choose the Make EXE file command, the BC compiler searches for a stand-alone (.LIB) library that corresponds to the loaded Quick library when it creates an executable file. Quick libraries provide fast access to your own custom library of procedures, but you can use them only inside the QuickBASIC environment. The compiler needs access to the corresponding stand-alone (.LIB) library to include the Quick library's procedures in an executable file. Therefore, it is a good idea to keep both kinds of libraries──Quick libraries and .LIB libraries──in the same directory. You can use the Options menu's Set Paths command to tell QuickBASIC where to look for any .LIB or Quick libraries it needs when creating an executable file. (The Make Library command on the Run menu makes both kinds of libraries automatically. See Section 16.6, "Make Library," in this manual and Appendix H in Programming in BASIC for more information on creating and using Quick libraries.) 16.5.3 Types of Executable Files You can create two different types of executable files, depending on whether or not you want your executable program to require access to the run-time module BRUN45.EXE. 16.5.3.1 Programs that Use the Run-Time Module Programs compiled with the EXE Requiring BRUN45.EXE option need access to the run-time module BRUN45.EXE when they run. The run-time module contains code needed to implement the BASIC language. Run-time modules provide the following advantages over stand-alone programs: ■ The executable file is much smaller. ■ COMMON variables and open files are preserved across CHAIN statements, allowing programs to share data. Stand-alone programs do not preserve open files or variables listed in COMMON statements when a CHAIN statement transfers control to another program. ■ The BRUN45.EXE run-time module resides in memory, so it does not need to be reloaded for each program in a series of chained programs. 16.5.3.2 Stand-Alone Programs When you use the Stand-Alone EXE File option, the executable file does not require access to the run-time module BRUN45.EXE. However, since files created with this option include the support routines found in BRUN45.EXE, they are larger than files created with the EXE Requiring BRUN45.EXE option. Also, files created with the EXE Requiring BRUN45.EXE option do not preserve open files or variables listed in COMMON statements when a CHAIN statement transfers control to another program. Stand-alone files have the following advantages: ■ Slightly faster execution than run-time programs. ■ RAM space may be saved if you have small, simple programs that do not require all the routines in the run-time module. ■ The program does not require the run-time module to run. This allows the program to run by itself on any DOS computer. 16.5.4 Run-Time Error Checking in Executable Files If you turn on the Produce Debug Code check box in the Make EXE File dialog box when you make an executable file, the following conditions are checked when the program runs: ■ Arithmetic overflow. All arithmetic operations, both integer and floating-point, are checked for overflow and underflow. ■ Array bounds. Array subscripts are checked to ensure they are within the bounds specified in DIM statements. ■ Line locations. The generated binary code includes additional tables so that run-time error messages indicate the lines on which errors occur. ■ RETURN statements. Each RETURN statement is checked for a prior GOSUB statement. ■ CTRL+BREAK, the keystroke combination to halt program execution. After executing each line, the program checks to see if the user pressed CTRL+BREAK. If so, the program stops. Note that you must compile a program with the Produce Debug Code option turned on if you want it to respond to CTRL+BREAK. Otherwise, CTRL+BREAK halts a program only when one of the following conditions is met: 1. A user enters data in response to an INPUT statement's prompt. 2. The program's code explicitly checks for CTRL+BREAK. ────────────────────────────────────────────────────────────────────────── WARNING If you don't use the Produce Debug Code option, then array-bound errors, RETURN without GOSUB errors, and arithmetic overflow errors do not generate error messages. Program results may be unpredictable. ────────────────────────────────────────────────────────────────────────── 16.5.5 Floating-Point Arithmetic in Executable Files When you compile a program into an executable file, the executable file does floating-point calculations more quickly and efficiently than the same program running in the QuickBASIC environment. Executable files optimize for speed and accuracy by changing the order in which they do certain arithmetic operations. (They also make greater use of a numeric coprocessor chip or emulation of a coprocessor's function.) One side effect of this extra accuracy in the results of relational operations is that you may notice a difference when comparing single- or double-precision values. For example, the following code fragment prints Equal when run in the QuickBASIC environment but Not Equal when it is run as an executable file: B!=1.0 A!=B!/3.0 . . . IF A!=B!/3.0 THEN PRINT "Equal" ELSE PRINT "Not Equal" This problem results from performing the calculation B!/3.0 inside a comparison. The compiled program stores the result of this calculation on the math coprocessor chip, which gives it a higher degree of accuracy than the value stored in the variable A!, causing the inequality. You can avoid such problems in comparisons by doing all calculations outside of comparisons. The following rewritten code fragment produces the same results when run in the environment and as an executable file: B!=1.0 A!=B!/3.0 . . . Tmp!=B!/3.0 IF A!=Tmp! THEN PRINT "Equal" ELSE PRINT "Not Equal" 16.6 Make Library Command (Full Menus Only) The Make Library command creates a custom Quick library for use with compiled programs. A Quick library can contain procedures that you wish to use in more than one program. When you make a library with QuickBASIC, consider whether the library is new or an update of an existing library. If it is an update, start QuickBASIC with the /L command-line option, supplying the name of the library to be updated as a command-line argument (for example, QB /L Mylib). You can also include the name of a program whose modules you want to put in the library. In this case QuickBASIC loads all the modules specified in that program's .MAK file. If it is a new library, start QuickBASIC first, and use Load File to load the files you want to convert into a library. If you load your program when starting QuickBASIC, be sure to unload any modules you do not want in the Quick library, including the main module (unless it contains procedures you want in the library). 16.6.1 Unloading and Loading Modules To keep your Quick libraries as compact as possible, remove any nonessential modules currently loaded. To remove ("unload") the unwanted modules, follow these steps: 1. Choose the Unload File command from the File menu. 2. Select the module you want to unload from the list box, then press ENTER. The module is unloaded, but still exists as a disk file. 3. Repeat steps 1 and 2 until you have unloaded all unwanted modules. Alternatively, start QuickBASIC with or without a library specification, and load only those modules you want. In this case, you load each module using the Load File command from the File menu. To load one module at a time, follow these steps: 1. Choose the File menu's Load File command. 2. Select the name of a module you want to load from the list box. 3. Repeat steps 1 and 2 until you have loaded all the modules you want. 16.6.2 Creating Libraries Once you load the previous library (if any) and the new modules you want to include in the Quick library, choose the Make Library command on the Run menu. The dialog box shown in Figure 16.3 appears. Name for library │ ┌────────────────────────────┼─ Make Library ────────────────────────────── │ ┌─┼──────────────────────────────────────────┐ │ Quick-Library File Name: │prntproc.lib │ │ └────────────────────────────────────────────┘ │ │ ┌─[X] Produce Debug Code ├─┼──────────────────────────────────────────────────────────────────────── │ │ < Make Library > < Make Library and Exit > < Cancel > < Help > └─┼──────────────────────────────────────────────────────────────────────── │ Provides additional debugging information when checked Figure 16.3 Make Library Dialog Box To create a Quick library after you have chosen the Make Library command, do the following: 1. Enter the name of the library you wish to create in the Quick-Library File Name text box. If you enter a base name (that is, a file name with no extension), Quick BASIC appends the extension .QLB when it creates the Quick library. If you want your library to have no extension, add a terminating period (.) to the base name. Otherwise, you may enter any unique base name and extension you like, as long as it is consistent with DOS file-name rules. 2. Select the Produce Debug Code check box only if you are specifically trying to track a bug you believe to be in a library you are updating. It makes your library larger, your program slower, and gives only a small amount of error information. 3. Create the Quick library: ■ Choose the Make Library command button if you want to remain in the environment after the Quick library is created. ■ Choose the Make Library and Exit command button if you want to return to the DOS command level after the Quick library is created. ────────────────────────────────────────────────────────────────────────── NOTE A Quick library that needs to trap events such as keystrokes must contain at least one event-trapping statement in one of its modules. This statement can be as simple as TIMER OFF, but without it, events are not trapped correctly in the Quick library. ────────────────────────────────────────────────────────────────────────── 16.7 Set Main Module Command (Full Menus Only) The Set Main Module command lets you select a main module from a list of the currently loaded modules. In a single-module program, the main module is the program. Therefore, as soon as you have typed your first statement and have saved it, you have created a main module. In a multiple-module program, the main module contains the first statement to be executed when the program is run──it is the first entry in any list box (such as the one in the SUBs command dialog box) that shows the modules in a program. If you start QuickBASIC without specifying a file name, the title bar of the View window contains the word Untitled. If you save the contents of that View window, even if it is empty, the name under which you save it becomes the name of the main module of the program. After you name the main module, the name appears in the title bar of the View window. 16.7.1 Changing the Main Module A module can be part of many different programs, but it can be the main module of only one program (the program bearing its name). As you are editing your program, you may find that you want to reorganize it and have execution begin with a module other than the one currently designated as the main module. To do this, follow these steps: 1. Choose the Set Main Module command from the Run menu. The Set Main Module dialog box contains a list of currently loaded modules. 2. Select the module you want to designate as the main module, and press ENTER. See Figure 16.4. Becomes new main module ┌─────── Set Main Module ───────┐ │ Choose new main module: │ │ ┌─────────────────────────┐ │ │ │ DEMO1.BAS │ │ │ TEST.BAS ▒ │ │ │ TORUS.BAS ▒ │ │ │ DEMO2.BAS ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ ▒ │ │ │ │ │ └─────────────────────────┘ │ │ │ ├───────────────────────────────┤ │ < OK > < Cancel > < Help > │ └───────────────────────────────┘ Figure 16.4 Set Main Module DIalog Box 16.7.2 The .MAK File When you save a multiple-module program QuickBASIC creates a special file containing the names of all the program modules. This file has the base name of the main module plus the extension .MAK. When you reload the program, QuickBASIC uses the .MAK file to locate all of the modules. For this reason, do not delete a .MAK file. If you move a multiple-module program to another directory, you also need to move the .MAK file. Only program modules are included in a .MAK file. The main program module is the first .MAK file entry. QuickBASIC does not add other types of files to the .MAK list. If your program relies on include files, the program must specify each file as an argument to a $INCLUDE metacommand. The .MAK file is a text file. If you wish to edit it, load it into QuickBASIC using the Document option of the File menu's Load File command. You can remove modules from a program's .MAK file without editing the .MAK file directly. With the program loaded, follow the module-unloading procedure outlined in Section 16.6.1, "Unloading and Loading Modules." When you save the program, the names of any unloaded modules are removed from the .MAK file. ──────────────────────────────────────────────────────────────────────────── Chapter 17 Debugging Concepts and Procedures This chapter introduces the topic of debugging your programs with QuickBASIC. QuickBASIC can help you track down errors that result from flaws in the logic of a program. This chapter provides the following information on debugging: ■ Using QuickBASIC to prevent bugs as you are writing your program ■ Debugging terms and concepts See Chapter 18, "The Debug Menu," for more information on debugging. 17.1 Debugging with QuickBASIC QuickBASIC simplifies debugging with advanced features such as breakpoints, watchpoints, instant watch, and watch expressions. Other fundamental tools include the STOP, PRINT, CONT, TRON, and TROFF statements. With QuickBASIC, you do not need to use separate tools or invoke any special options to debug your program. When you notice a bug, you can start tracking it immediately. The QuickBASIC environment contains everything you need. Additionally, QuickBASIC does not require you to recompile or relink a program after making a change. You can usually run a program to the point where a problem occurs, suspend execution, fix the problem, and continue running the program as though it never stopped. In QuickBASIC, you debug as you program. 17.2 Preventing Bugs with QuickBASIC Preventing bugs is the best way to have a bug-free program. Here are three ways to prevent bugs: 1. Design your program carefully. An important rule in good program design is to isolate different tasks by writing SUB or FUNCTION procedures to perform those tasks. A small procedure is much easier to debug than a large program without procedures. An additional benefit of using procedures is that you can save groups of procedures in a separate file called a module, then use them in other programs that perform the same tasks. (See Chapter 2, "SUB and FUNCTION Procedures," in Programming in BASIC for more information on procedures and modules.) 2. Use the Immediate window. As you program, use the Immediate window at the bottom of the QuickBASIC screen to isolate and test small pieces of the program. See Section 17.3.5 for more information on the Immediate window. When these pieces work on their own, move them into the View window. 3. Run your program often. Because QuickBASIC checks and translates each statement to executable code (instructions understood by the computer) after you type a line and press ENTER, you can continually test-run the program as you add new pieces. This helps catch simple bugs that could be difficult to track in a finished program. Suppose you have written a program that contains the following code: DIM Array$(1 TO 20) . . . I% = 1 DO INPUT Temp$ IF Temp$ <> "" THEN Array$(I%) = Temp$ I% = I + 1 END IF LOOP UNTIL Temp$ = "" OR I% > 20 You believe you have designed a logical loop. Now you can test the code by doing the following: 1. Execute the loop and enter text when prompted. (To end the loop, press ENTER instead of entering text.) 2. Type the following in the Immediate window: For I% = 1 to 20: PRINT Array$(I%): NEXT Your output will alert you to a flaw in your program──the variable I% is not incrementing. Upon closer inspection, you notice that you must change the line I% = I + 1 to I% = I% + 1 Along with designing your program carefully, using the Immediate window, and running your program often, another debugging technique is setting a "watch expression." This allows you to "watch" (monitor) the value of the variable I% as you trace through the loop. Section 17.3.3, "Watch Expressions," and Section 17.3.4, "Watch Window," tell how to watch an expression while a program is executing. 17.3 QuickBASIC's Debugging Features This section defines some key debugging terms and concepts. See Chapter 18, "The Debug Menu," for information on the Debug menu and how to use QuickBASIC's debugging commands. 17.3.1 Tracing (Full Menus Only) The Trace On command highlights each statement as it executes. If the program manipulates the screen, QuickBASIC switches back and forth between the highlighted statements and the output screen (this is referred to as "animated execution"). For example, with tracing on you can follow branching in an IF...THEN...ELSE statement. QuickBASIC's tracing options let you run the entire program at once (normal tracing), one statement at a time (single stepping), or one procedure at a time (procedure stepping). See Section 17.3.6, "Other Debugging Features," for a discussion of single stepping and procedure stepping. Turning on tracing automatically enables QuickBASIC's History On command. History records the last 20 statements executed so you can stop execution and trace backward and forward through the 20 previous statements with History Back and History Forward. The history feature allows you to answer the question, "How did I get here?" See Also Section 18.6, "Trace On Command"; Section 18.7, "History On Command" 17.3.2 Breakpoints and Watchpoints A breakpoint is a location in your program where you want execution to pause. With breakpoints, you can set your program to execute only as far as you want, letting you test one segment of your program at a time. You can also use breakpoints to stop the program at strategic places and then examine a variable's value. A watchpoint is an expression that stops a program when the expression becomes true (nonzero). You might use a watchpoint, for example, if your program crashes in a loop that increments X from 1 to 50. A watchpoint of X=49 stops the program when X becomes 49. You can then single step the program through the forty-ninth loop to locate the particular statement that causes the crash. Watchpoints appear in the Watch window. The Watch window displays all of the current watchpoints and watch expressions. See Also Section 17.3.4, "Watch Window"; Section 18.1, "Add Watch Command"; Section 18.8, "Toggle Breakpoint Command" 17.3.3 Watch Expressions Watch expressions, which are entered with the Add Watch command, let you observe the value of a variable (a number or text string) or the condition of an expression (true or false) in an executing program. For example, if you want to watch the value of a variable MyVar and an expression X=1, QuickBASIC places MyVar and X=1 in the Watch window. As the program runs, QuickBASIC displays the changing values of MyVar and the condition of X=1 (-1 for true, 0 for false) in the Watch window. If a program MYPROG.BAS initially assigns MyVar a value of 10 and X a value of 1, then the Watch window displays MYPROG.BAS MyVar: 10 MYPROG.BAS X=1: -1 If the program later changes MyVar to 99 and X to 3, the Watch window will then display MYPROG.BAS MyVar: 99 MYPROG.BAS X=1: 0 The Instant Watch command displays the value of the variable or expression containing the cursor in a dialog box──you do not need to open the Watch window. However, the Instant Watch dialog box does give you the option of adding the variable or expression to the Watch window. See Also Section 17.3.4, "Watch Window"; Section 18.1, "Add Watch Command"; Section 18.2, "Instant Watch Command" 17.3.4 Watch Window The Watch window is the window that opens at the top of the QuickBASIC screen to let you track watchpoint conditions or watched expressions during program execution. The current value or condition (true or false) of a variable or expression can be displayed in the Watch window only when the program is executing in the part of the program in which the watchpoint or watch expression was added. The message Not watchable is displayed at all other times. For example, suppose you create a watch expression to monitor the value of a variable MyVal while you are working on a procedure called MySub. The value of MyVal will appear in the Watch window only when the program executes the MySub procedure. At any other time──when execution is in the module-level code or other procedures──the message Not watchable appears after MyVal in the Watch window. Even if a program uses a SHARED statement to share a variable between the module level and the procedure level, that variable is watchable only at the level that was active when the variable was added to the Watch window. Nothing is watchable while a DEF FN function is active. See Also Section 17.3.3, "Watch Expressions"; Section 18.1, "Add Watch Command"; Section 18.2, "Instant Watch Command" 17.3.5 Immediate Window The Immediate window is the window at the bottom of the screen. In it you can execute BASIC statements directly to gain information useful in debugging. Note, however, that the Immediate window can access information only about those variables in the part of the program (module or procedure) that is currently active. For example, if you suspend a program in a procedure, you may use the Immediate window to access local and global variables and expressions (indicated by the SHARED statement) but not ones local only to the module-level code or another procedure. See also Section 10.5, "Using the Immediate Window" 17.3.6 Other Debugging Features Table 17.1 describes several additional debugging features available in QuickBASIC Version 4.5. Some are intended to be used together, while others are generally used by themselves. Table 17.1 Additional Debugging Features ╓┌─┌──────────────┌──────────────┌───────────────────────────────────────────╖ Feature How to Execute Description ────────────────────────────────────────────────────────────────────────── Break on Choose from Locates errors in programs using error Feature How to Execute Description ────────────────────────────────────────────────────────────────────────── Break on Choose from Locates errors in programs using error Errors command the Debug menu handling. Break on Errors disables error handling and halts execution when an error occurs. Press SHIFT<|>+<|>F8 (History Back) to see the error-causing statement. Execute to Press F7 Executes from the beginning of a program up cursor to and including the line containing the cursor, and then halts execution. Use this feature to quickly execute to a problem-causing section of code, and then single step to find the error. Set Next Choose from Changes the execution sequence of an Statement the Debug menu interrupted program so that the next command statement to execute will be the one at the cursor. If your program encounters an error that you can correct immediately, use Set Next Statement to tell QuickBASIC to begin Feature How to Execute Description ────────────────────────────────────────────────────────────────────────── Next Statement to tell QuickBASIC to begin executing from the corrected line when you choose Continue. Single Press F8 Executes a single statement. This is a stepping powerful tool for debugging code. By single stepping and using the Watch window together, you can gain a thorough understanding of how each statement affects your variables. Procedure Press F10 Executes a procedure call and the procedure stepping as a single statement. If you are single stepping and encounter a procedure you know works properly, procedure stepping lets you execute the entire procedure at once (rather than single stepping through it). ────────────────────────────────────────────────────────────────────────── Feature How to Execute Description ────────────────────────────────────────────────────────────────────────── See Also Section 18.10, "Break On Errors Command"; Section 18.11, "Set Next Statement Command" ──────────────────────────────────────────────────────────────────────────── Chapter 18 The Debug Menu The Debug menu controls features that speed program debugging. These features let you watch variables and expressions as they change, trace program execution, stop the program at specified locations or on specified conditions, and alter the restart location of a suspended program. The Debug menu contains the following commands: ■ Add Watch. Displays the values of variables and expressions in the Watch window as a program executes. ■ Instant Watch. Displays the value of a variable or expression. ■ Watchpoint. Allows you to halt program execution when a condition you specify becomes true (Full Menus only). ■ Delete Watch. Removes an item from the Watch window. ■ Delete All Watch. Removes all entries in the Watch window and closes the window (Full Menus only). ■ Trace On. Steps through the program in slow motion, highlighting the currently executing statement (Full Menus only). ■ History On. Records the last 20 lines executed by the program (Full Menus only). ■ Toggle Breakpoint. Turns breakpoints on and off. ■ Clear All Breakpoints. Removes all previously set breakpoints. ■ Break on Errors. Sets an implicit breakpoint at the most recent error-handling statement (Full Menus only). ■ Set Next Statement. Changes the program execution sequence so that the next statement executed is the one at the cursor (Full Menus only). 18.1 Add Watch Command The Add Watch command displays the values of variables and expressions as the program executes. QuickBASIC opens a Watch window at the top of the screen to accommodate the variables. To use the command, choose Add Watch on the Debug Menu. A dialog box appears. Type in the name of the variable or expression you want to watch. See Figure 18.1. Variable or expression │ File Edit View Search │Run Debug Calls Options Help SORTDEMO.BAS Z > 100: │ SORTDEMO.BAS Length > 50: │ ┌───────────────────────────┼── SORTDEMO.BAS ─────────────────────────┤├── │' Define the data type used│to hold the information for each colored bar: │ TYPE SortType │ │ Length┌───────────────┼────── Add Watch ───────────────────────┐ │ │ │ │ │ ColorV│ Enter expression to be added to Watch window: │ │ BarStr│ │ │ │ ENDTYPE │ ┌────────────┼─────────────────────────────────────┐ │ │ │ │COLORVAL ───┘ │ │ │' Declare g│ └──────────────────────────────────────────────────┘ │ │ CONST FAL├────────────────────────────────────────────────────────┤ │ CONST NUM│ < OK > < Cancel > < Help > │ │ └────────────────────────────────────────────────────────┘ │' Declare global variables, and allocate storage space for them. SortArray │' and SortBackup are both arrays of the data type SortType defined above: │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── │ │ F1=Help Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item Figure 18.1 Add Watch Dialog Box Watching a variable in the Watch window avoids repeated use of PRINT statements for tracking the variable's value. You can also watch the condition (true or false) of an expression in the Watch window. True is represented by -1; false by 0. The variables or expressions you are watching are easily removed from the Watch window when debugging is complete. During program execution, a value in the Watch window changes when its value in the program changes. Sometimes the message Not watchable may appear rather than a value. This means that the debugger cannot currently access the variable because program execution is not in the part of the program (the procedure- or module-level code) from which the variable was added to the Watch window. A variable is watchable only when the program is executing in the part of the program from which the variable was added to the Watch window. Note that if you are interested in only one or two instances of a variable's value, it may be easier to use the Instant Watch command, described in Section 18.2. Example The following example calculates the nth number in a sequence known as the Fibonacci sequence. In the Fibonacci sequence, each number is the sum of the two preceding numbers, beginning with 1 and 2. The first 10 Fibonacci numbers are 1, 2, 3, 5, 8, 13, 21, 34, 55, and 89. This example uses the Add Watch command and animated tracing (the process of switching back and forth between highlighted statements in your program and the output screen). 1. Start QuickBASIC or choose the New Program command from the File menu, and type: DEFINT A-Z INPUT n PRINT Fib(n) END 2. Choose the Add Watch command from the Debug menu, then enter n in the text box. This displays the value n has at the module level. 3. Create a FUNCTION procedure called Fib by choosing the New FUNCTION command from the Edit menu and typing Fib in the dialog box. (DEFINT A-Z is automatically added above the first line of the FUNCTION definition because of the DEFtype statement you typed in step 1.) Now enter the procedure as follows: FUNCTION Fib(n) IF n > 2 THEN Fib = Fib(n - 1) + Fib(n - 2) ELSE Fib = n END IF END FUNCTION 4. Choose the Add Watch command on the Debug menu, and again add n to the Watch window. This displays the value of n within the Fib procedure. 5. Choose the Trace On command on the Debug menu. 6. Choose Start on the Run menu to execute the program. 7. Enter 8 after the input prompt. Observe the Watch window to see how n changes as the procedure recursively calls itself to calculate the eighth number in the Fibonacci sequence. 8. Choose the Output Screen command (or press F4) to see the program results. See Also Section 17.3.3, "Watch Expressions"; Section 17.3.4, "Watch Window" 18.2 Instant Watch Command The Instant Watch command displays the value of a variable or the condition of an expression (true or false) in a dialog box. Use the command by moving the cursor within (or to the right of) a variable or selecting an expression and then choosing Instant Watch on the Debug menu. QuickBASIC displays a dialog box with the variable or expression in the upper text box and the value or condition (-1 for true, 0 for false) in the lower text box. See Figure 18.2. Variable or expression │ File Edit View Search │Run Debug Calls Options Help SORTDEMO.BAS Z > 100: │ SORTDEMO.BAS Length > 50: │ ┌───────────────────────────┼── SORTDEMO.BAS ─────────────────────────┤├── │' Define the data type used│to hold the information for each colored bar: │ TYPE SortTyp┌────────────┼────── Add Watch ─────────────────┐ │ Length AS│ │ │ed │ │ ┌─────────┼───────────────────────────────┐ │ │ ColorVal │ │Colorval─┘ │ │ │ BarString│ └─────────────────────────────────────────┘ │ters) │ ENDTYPE │ │ │ │ ┌─────────────────────────────────────────┐ │ │' Declare glob│ │ 0 ──┐ │ │ │ CONST FALSE │ └─────┼───────────────────────────────────┘ │ │ CONST NUMOP ├────────┼──────────────────────────────────────┤ │ T│ < Add│Watch > < Cancel > < Help > │ │' Declare glob└────────┼──────────────────────────────────────┘. SortArray │' and SortBackup are both arrays of the data type SortType defined above: │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├───────────────────────┼─────── Immediate ──────────────────────────────── │ │ │ │ F1=Help Enter=Execute │Esc=Cancel Tab=Next Field Arrow=Next Item │ Value or condition Figure 18.2 Instant Watch Dialog Box Use the Instant Watch command for debugging assignment statements and for checking variables or expressions. If you need to watch a variable or expression constantly, use the Add Watch command (or press the Add Watch button in the Instant Watch dialog box) to add the item to the Watch window. The Instant Watch command is convenient for displaying a value or condition in a suspended or stopped program. Shortcut Key SHIFT+F9 See Also Section 17.3.3, "Watch Expressions"; Section 17.3.4, "Watch Window" 18.3 Watchpoint Command (Full Menus Only) The Watchpoint command allows you to set a watchpoint──an expression that halts program execution when the expression becomes true (for example, when the value of a variable X equals 100). QuickBASIC displays the watchpoint in the Watch window. When you choose the Watchpoint command a dialog box appears. You can enter any variable name or expression along with relational operators in the Watchpoint text box. See Figure 18.3. File Edit View Search Run Debug Calls Options Help SORTDEMO.BAS Z > 100: SORTDEMO.BAS Length > 50: ┌────────────────────────────── SORTDEMO.BAS ─────────────────────────┤├── │' Define the data type used to hold the information for each colored bar: │ TYPE SortType │ Length┌───────────────────── Watchpoint ───────────────────────┐ │ │ │ │ ColorV│ Enter expression (will break when TRUE): │ │ BarStr│ │ │ ENDTYPE │ ┌──────────────────────────────────────────────────┐ │ │ ┌──┼──COLORVAL = 10 │ │ │' Declar│ g│ └──────────────────────────────────────────────────┘ │ │ CONST │AL├────────────────────────────────────────────────────────┤ │ CONST │UM│ < OK > < Cancel > < Help > │ │ │ └────────────────────────────────────────────────────────┘ │' Declar│ global variables, and allocate storage space for them. SortArray │' and So│tBackup are both arrays of the data type SortType defined above: │▒▒▒▒▒▒▒│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├────────│────────────────────── Immediate ──────────────────────────────── │ │ │ │ F1=Help │Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item │ Condition that will halt the program Figure 18.3 Watchpoint Dialog Box QuickBASIC's relational operators include =, <>, >, <, >=, and <=. If an expression is entered without a relational statement, QuickBASIC assumes the relation <> 0. QuickBASIC then suspends execution of the program as soon as the expression becomes a nonzero value. If you set a watchpoint in a SUB or FUNCTION procedure, the Watch window describes the given expression as TRUE or FALSE only when the program is executing in that procedure. At all other times the message Not watchable will appear beside the watchpoint in the Watch window. Similarly, watchpoints at the module level display the message Not watchable when execution is in a procedure. See Also Section 17.3.2, "Breakpoints and Watchpoints"; Section 18.1, "Add Watch Command"; Section 18.4, "Delete Watch Command" 18.4 Delete Watch Command The Delete Watch command removes an item from the Watch window. The Delete Watch dialog box, shown in Figure 18.4, displays the current Watch-window items and allows you to select which Watch-window item to delete. List of items currently in Watch window │ │ File Edit View Search Run Debug Calls Options Help │┌SORTDEMO.BAS Z > 100: 0 └┤SORTDEMO.BAS ColorVal: 0 └SORTDEMO.BAS Length < 50: -1 ┌──────────────┌───────────────── Delete Watch ────────────────┐──────┤├── │' Define the d│ ┌─────────────────────────────────────────┐ │lored bar: │ TYPE SortTyp│ │ SORTDEMO.BAS Z > 100: │ │ Length AS│ │ SORTDEMO.BAS ColorVal: ▒ │ed │ │ │ │ SORTDEMO.BAS Length < 50: ▒ │ │ ColorVal │ │ │ ▒ │ │ BarString│ │ │ ▒ │ters) │ ENDTYPE │ │ │ ▒ │ │ │ │ │ ▒ │ │' Declare glob│ │ │ ▒ │ │ CONST FALSE │ │ │ │ │ CONST NUMOP │ └─┼───────────────────────────────────────┘ │ │ T│ │ │ │' Declare glob├────┼──────────────────────────────────────────┤. SortArray │' and SortBack│ │ < OK > < Cancel > < Help > │ned above: │▒▒▒▒▒▒▒▒▒▒▒▒▒└────┼──────────────────────────────────────────┘▒▒▒▒▒▒▒▒▒▒ ├───────────────────┼─────────── Immediate ──────────────────────────────── │ │ F1=Help Enter=Execute Esc=Cancel Tab=Next Field Arrow=Next Item │ Item to remove Figure 18.4 Delete Watch Dialog Box Use the Delete All Watch command to remove all Watch-window items at once. See Also Section 18.5, "Delete All Watch Command" 18.5 Delete All Watch Command (Full Menus Only) The Delete All Watch command in the Debug menu removes all of the Watch-window entries and closes the window. You typically use the Delete All Watch command when the section of program code you are working on runs properly. If you want to selectively remove Watch-window items, use the Delete Watch command. See Also Section 18.4, "Delete Watch Command" 18.6 Trace On Command (Full Menus Only) The Trace On command steps through the program in slow motion, highlighting the executing statement. When this command is active, a bullet (■) appears next to the Trace On command on the Debug menu. Choosing Trace On again toggles the feature off. Trace On is a useful method for determining whether the general flow of your program is what you intended, especially if you use it in combination with watchpoints, breakpoints, and CTRL+BREAK (which suspends execution). Trace On also records the last 20 statements executed, so you can review them with the History Back and History Forward commands (see Sections 18.7.1 and 18.7.2). If a program sends output to the screen, running it with Trace On active causes the screen to flash back and forth between QuickBASIC and the output screen. You can use the Output Screen command from the View menu to control which screen appears during program suspension (see Section 14.5). See Also Section 18.1, "Add Watch Command"; Section 18.7, "History On Command"; Section 18.8, "Toggle Breakpoint Command" 18.7 History On Command (Full Menus Only) Choose the History On command from the Debug menu to record the last 20 lines executed by the program the next time it runs. When this command is active, a bullet (■) appears next to the History On command on the Debug menu. Execution speed is slower with this feature active. The History On command allows you to trace backward and forward through the last 20 statements executed by the program. This is particularly useful when you get a run-time error and you want to see which 20 statements were executed immediately preceding the error. Checking the execution history also lets you review the specific branching of a program through nested sequences of conditional structures like IF...THEN...ELSE statements. Use History On in conjunction with breakpoints to review groups of up to 20 consecutive statements in your program. You use History On with the History Back and History Forward commands (see Sections 18.7.1 and 18.7.2). ────────────────────────────────────────────────────────────────────────── NOTE The History commands do not execute statements. They just show the previous execution sequence. ────────────────────────────────────────────────────────────────────────── 18.7.1 History Back Activated with SHIFT+F8, History Back steps back in your program through the last 20 program statements recorded by either the History On or Trace On command. When you wish to review the flow of a program, interrupt the program execution by pressing CTRL+BREAK; then press SHIFT+F8 to check back through the last 20 statements executed. This shows you the program flow through statements and is particularly useful for following conditional branches. 18.7.2 History Forward Activated with SHIFT+F10, History Forward lets you step forward in your program through the last 20 program statements. You can use History Forward only after using History Back. Because History Back shows the reverse execution order, step backward first, and then watch the execution sequence using History Forward. See Also Section 18.6, "Trace On Command" 18.8 Toggle Breakpoint Command The Toggle Breakpoint command turns a breakpoint (a specific location in the program where execution stops) on and off. The Toggle Breakpoint command affects the line containing the cursor. Lines on which breakpoints are set appear in reverse video. Use a breakpoint to pause at points where you suspect problems in your program, then test the values of variables to confirm or refute your suspicion (in the Immediate window). Alternately, insert a breakpoint prior to a problem area and then use single stepping (see Section 17.3.6, "Other Debugging Features," for a description of single stepping) or use the Instant Watch command for a detailed view of program flow and variable values. Clear a breakpoint on the current cursor line by selecting Toggle Breakpoint again. Shortcut Key F9 See Also Section 17.3.2, "Breakpoints and Watchpoints"; Section 18.9, "Clear All Breakpoints Command" 18.9 Clear All Breakpoints Command The Clear All Breakpoints command removes all breakpoints in a program. Remove individual breakpoints (while leaving others in place) with the Toggle Breakpoint command. You typically use the Clear All Breakpoints command when you know a section of program code runs properly. See Also Section 17.3.2, "Breakpoints and Watchpoints"; Section 18.8, "Toggle Breakpoint Command" 18.10 Break on Errors Command (Full Menus Only) The advanced debugging command Break on Errors allows you to trace an error-causing statement in a program that uses error handling. When toggled on (indicated by a bullet beside the command), Break on Errors sets an implicit breakpoint after the label specified in the most recently executed error-handling (ON ERROR) statement. If you do not use error handling, you will not need this command. When an error occurs in a program with error handlers, QuickBASIC routes execution to the label specified in the appropriate ON ERROR statement. If there is no ON ERROR statement that explicitly addresses the type of error QuickBASIC encounters, finding the source of the error can be difficult. Break on Errors solves this error-finding problem. The Break on Errors command enables History On and records the statement that caused the error. Choosing History Back (SHIFT+F8) shows you the error-causing statement. In the following program fragment, an error occurs at the line Y=5/X. This example demonstrates how QuickBASIC uses Break on Errors to stop after the label specified in the most recent ON ERROR statement: ON ERROR GOTO FirstHandler 'First error handler ON ERROR GOTO NextHandler 'Second error handler ON ERROR GOTO LastHandler 'Third and last error handler . X = 0 Y = 5/X . LastHandler: 'Label in most recently executed error handler . 'QuickBASIC stops immediately after label . With Break on Errors on, an error transfers program flow to LastHandler and execution stops. History Back will now show you the statement that caused the error. See Also Section 18.7, "History On Command" 18.11 Set Next Statement Command When you want to skip over or rerun a section of a program, halt execution, then use the Set Next Statement command. The Set Next Statement command changes program execution sequence so that the next statement executed is the one at the cursor. QuickBASIC ignores any intervening program code. Use the Set Next Statement command with care; skipping code can lead to undefined variables and result in errors. The effect of the Set Next Statement command is similar to that of a GOTO statement, and the same restrictions apply. For example, you cannot branch to the middle of a procedure from the module level of a program. Note that the Next Statement command on the View menu moves the cursor to the next statement to be executed when the program continues to run, while the Set Next Statement command on the Debug menu allows you to establish (set) the next statement to be executed. Next Statement is used to indicate which statement will execute next if no changes are made; Set Next Statement allows you to alter this by choosing a new resumption point for program execution. See Also Section 14.4, "Next Statement Command" ──────────────────────────────────────────────────────────────────────────── Chapter 19 The Calls Menu (Full Menus Only) The Calls menu is an advanced feature that shows all of the procedure calls that led to the current execution location. It lets you do the following: ■ See the sequence of nested procedure calls your program executed in order to arrive at the current procedure. ■ Continue your program from the point execution stopped to any listed procedure. Use the Calls menu to see which procedures execution passed through. During debugging, you can use the Calls menu and single stepping (described in Section 17.3.6, "Other Debugging Features") together to execute up to an error, recreating the same variable values and conditions that led to a program crash. If your procedures do not call other procedures, the Calls menu shows only the name of the main module and any currently executing procedure. In any program, the Calls menu displays only the program name prior to running. 19.1 Using the Calls Menu The Calls menu shows calls between procedures. The following example illustrates the use of the Calls menu for both debugging and executing. Suppose you want to write a program to draw histograms (bar charts) on the screen, and you want your user to specify the fraction of the screen the chart will fill. Since you believe strongly in the use of structured programming, you break the process into several procedures. Your main module prompts your user for data and then calls a procedure DrawHisto to draw the chart. DrawHisto then sends the task of drawing the chart's bars to a separate procedure, DrawBars. Since the number of bars in the chart can vary (depending on the data your user entered), DrawBars farms out the job of calculating how wide each bar will be to the procedure CalcBarWidth. However, before CalcBarWidth can determine how wide each bar needs to be, it needs to know the width of the histogram. So, CalcBarWidth calls the procedure CalcHistoWidth which calculates the width of the screen to be used in the histogram. During execution, DrawHisto calls DrawBars, DrawBars calls CalcBarWidth, and CalcBarWidth calls CalcHistoWidth. If your program stops running inCalcHistoWidth, the Calls menu items appear in the order shown in Figure 19.1. ┌────────────────────────────────────────────────────────────────────────── │ │ ┌───────┐ │ │ Calls │ │ ├───────┴────────┐ │ │ CalcHistoWidth─┼─────Procedure in which the program stopped running │ │ CalcBarWidth │ │ │ DrawBars │ │ │ DrawHisto │ │ │ HISTOGRM.BAS───┼─────Location of first call │ └────────────────┘ │ │ HISTOGRM.BAS─DrawHisto─DrawBars─CalcBarWidth─CalcHistoWidth │ └────────────────────────────────────────────────────────────────────────── Figure 19.1 Sequence of Procedures on Calls Menu The Calls menu provides you with a "trail" you can follow to understand how your program executed to the CalcHistoWidth procedure; it is particularly valuable when your program stops in a series of deeply nested procedures (as in the histogram example). The order of the items in the Calls menu tells you the order in which the procedures were called; the item at the top of the list was called by the second item, the second item was called by the third item, the third item was called by the fourth item, etc. The first menu item is the one that was most recently executed. When a procedure crashes, the Calls menu gives you the sequence of procedures that led to the crash. Suppose the program you write to draw histograms (described earlier in this section) crashes in the CalcHistoWidth procedure. The Calls menu can help you continue the program or recreate the conditions that led to the crash. To continue the program through the rest of the CalcHistoWidth procedure, follow these steps: 1. Use the Immediate window to change any variables necessary to allow the program to run (that is, correct the error that caused the program to crash). 2. Choose CalcBarWidth from the Calls menu and press ENTER. This places the CalcBarWidth procedure in the View window, with the cursor on the line just after the line that called CalcHistoWidth. 3. Press F7. This runs the program from the current execution point (the statement where the program crashed) to the current cursor location (just after the call to CalcHistoWidth). The remaining code is executed in the CalcHistoWidth procedure and stops executing at the cursor in CalcBarWidth. 4. Use the Watch window, Immediate window, or Instant Watch command to verify that the variables have the values you desire, or use the Output Screen command to check any screen changes. Either way, you can verify that the program──with the changes you made in step 1──now runs properly. To recreate the conditions that led to the crash: 1. Move the cursor to the beginning of the program and choose the Set Next Statement command on the Debug menu. This prepares the program to run. 2. Choose CalcBarWidth in the Calls menu and press ENTER. QuickBASIC displays the CalcBarWidth procedure, with the cursor on the line below the call to CalcHistoWidth. Move the cursor to the line above the call to CalcHistoWidth. 3. Press F7. This runs the program from the current execution point (the first executable statement in the program) to the current cursor location. 4. Single step (press F8) from CalcBarWidth into CalcHistoWidth until you find the error-causing statement. 5. Use the Instant Watch command or other debugging techniques to resolve the error. In complex programs, using the Calls menu can simplify debugging. 19.2 Active Procedures The procedure at the top of the Calls menu is the currently active procedure. The one directly below it is the procedure that called the active procedure (and the one to which control returns when QuickBASIC leaves the active procedure). You can execute your program to any procedure in the Calls menu by choosing the procedure's name and pressing F7. Consider the procedures shown in Figure 19.1. Since CalcBarWidth is high-lighted, pressing ENTER and then F7 executes code from the beginning of the program to the statement in CalcBarWidth that follows the call to CalcHistoWidth. Note that QuickBASIC tracks only the most recent execution with the Calls menu, so that DrawBars would now be at the top of the list and CalcBarWidth and CalcHistoWidth would be removed (they were not involved in the most recent program execution). The Calls menu is a "stack" in that it displays the most recently called procedure on the top of the list. The Calls menu displays only the eight most recent procedures; any deeper nesting is not displayed until you start executing to return through the sequence of procedure calls. You can experiment with the characteristics of the call stack using the Fibonacci example at the end of Section 18.1, "Add Watch Command." Because the Fib procedure is recursive, the number you enter at the prompt determines the depth of the call stack and the number of procedures in the Calls menu. After interrupting execution (either by using a watchpoint or pressing CTRL+BREAK), you can display the Calls menu and use the methods described above to see the different iterations of the Fib procedure. Since the procedure is recursive, all the procedure names are identical. Each one listed represents another instance of the call. ──────────────────────────────────────────────────────────────────────────── Chapter 20 The Options Menu The Options menu controls some of QuickBASIC's special features, including those that customize the QuickBASIC screen, set default search paths, determine the function for the right mouse button, toggle syntax checking off and on, and switch between Full Menus and Easy Menus. The Option menu commands are listed below: ■ Display. Customizes the appearance of the QuickBASIC environment (colors, scroll bars, tab stops). ■ Set Paths. Sets default search paths depending on file type. ■ Right Mouse. Changes effect of clicking the right mouse button (Full Menus only). ■ Syntax Checking. Toggles syntax checking on and off (Full Menus only). ■ Full Menus. Toggles Full Menus on and off. When you alter the QuickBASIC environment, either by starting QuickBASIC with a command-line option (described in Section 10.1.1, "The QB Command") or by using the Options menu, QuickBASIC saves your modifications in a file that is called QB.INI. If the file already exists when you make changes, it is updated; if it does not exist, QuickBASIC creates it. QuickBASIC uses its default settings in the absence of the QB.INI file. 20.1 Display Command When you choose the Display command, the Display dialog box appears. It allows you to set the background color, foreground color, and the number of spaces the TAB key advances the cursor in the View window. The dialog box also lets you decide whether or not scroll bars appear in the View window. See Figure 20.1. Types of text to change Color options for Color options │ foreground text for backgroun ┌┼─────────────────────────────── Display ──┼──────────────────────────┼─── ││ ┌────────────────────────────── Colors ──┼──────────────────────────┼┐ ││ │ │ Foreground Background ││ ││ │ │ ┌─────────┐ ┌─────────┐ ││ ││ │ ┌(∙) 1. Normal Text │┌┼─Black │ Black ┐││ ││ │ │ └┤│ White ▒ │ White ▒├┘│ │└─┼─┤( ) 2. Current Statement ││ Gray ▒ │ Gray ▒│ │ │ │ │ └┼─BrWhite ▒ │ BrWhite ▒┘ │ │ │ └( ) 3. Breakpoint Lines │ ▒ │ ▒ │ │ │ │ ▒ │ ▒ │ │ │ │ ▒ │ ▒ │ │ │ │ │ │ │ │ └─────────┘ └─────────┘ │ │ │ │ │ └────────────────────────────────────────────────────────────────────┘ │ │ ┌───────────────────────── Display Options ──────────────────────────┐ │ │ [X] Scroll Bars Tab Stops: 8 │ │ └─────┼─────────────────────────────────────────────────────┼────────┘ ├────────┼─────────────────────────────────────────────────────┼─────────── │ │ < OK > < Cancel > < Help > │ └────────┼─────────────────────────────────────────────────────┼─────────── Turn scroll bars on when checked Number of spaces the TAB key advances Figure 20.1 Display Dialog Box Follow these steps to change the background and foreground colors: 1. Move the cursor to the parentheses preceding the color setting you want to change (Normal Text, Current Statement, or Breakpoint Lines). 2. Press TAB. The cursor moves to the Foreground Color list box. Use the DIRECTION keys to select the new foreground color for the item you chose in step 1. The list box item you have selected changes to reflect the colors you choose. 3. Press TAB again to move to the Background Color list box, then repeat the color selection process in step 2 for the background color. 4. Press ENTER. QuickBASIC now reflects your changes. The Display Options portion of the Display dialog box controls the scroll bar and TAB key settings. You can turn the View window's scroll bars on and off by pressing the SPACEBAR when your cursor is in the Scroll Bars check box (the default setting is "on"). The Tab Stops option controls the number of spaces the TAB key advances the cursor. Use the setting you find most helpful for improving the readability of your programs. 20.2 Set Paths Command The Set Paths command changes the default search paths for specified types of files. You may want to keep all files of a particular type within a single directory for organizational purposes. For example, you might wish to keep all of QuickBASIC's libraries and any of your own Quick libraries within a specific subdirectory or subdirectories of your QuickBASIC disk or directory. Since the environment requires access to its libraries, you would ordinarily need to provide a path name for each library used. The Set Paths dialog box lets you type in a search path (up to 127 characters) for your files. This saves you from fully qualifying each path name every time you access a library or other files not in the current working directory. For example, suppose you keep all of your include files and programs in a directory named QB──BI, which is in a directory named QB──45 on a disk in your A drive. You would take the following steps to direct QuickBASIC to automatically look in that directory any time it searched for a file with the .BI or .BAS extension: 1. Choose the Set Paths command on the Options menu. A dialog box appears. 2. Press the TAB key to move the cursor to the Include files text box. 3. Type in the path name: A: QB──45QB──BI See Figure 20.2. Path to directory containing files │ ┌───────────────────────────── Set Paths ───┼─────────────────────────── │ Search Path For: │ │ ┌─ ┌──────────────────────┼─────────────────────────── │ │Executable files: │ │ │ │ (.EXE, .COM) └──────────────────────┼─────────────────────────── │ │ │ │ │ ┌──────────────────────┼─────────────────────────── │ │Include files: │A;\QB_45\QB_BI ───────┘ │ │ (.BI, .BAS) └────────────────────────────────────────────────── │┌┤ │││ ┌────────────────────────────────────────────────── │││Library files: │ │││ (.LIB, .QLB) └────────────────────────────────────────────────── │││ │││ ┌────────────────────────────────────────────────── │││Help file: │ ││└─(.HLP) └────────────────────────────────────────────────── ├┼────────────────────────────────────────────────────────────────────── ││ < OK > < Cancel > < Help > └┼────────────────────────────────────────────────────────────────────── │ File types Figure 20.2 Set Paths Dialog Box 4. Press ENTER. ────────────────────────────────────────────────────────────────────────── NOTE The search paths you enter in the Set Paths dialog box do not change paths or environment variables previously set at the DOS level with the DOS PATH and SET commands. However, paths set with Set Paths are in effect whenever you are using QuickBASIC. ────────────────────────────────────────────────────────────────────────── 20.3 Right Mouse Command (Full Menus Only) The Right Mouse command lets you change the effect of clicking the right mouse button. When you choose the Right Mouse command, the dialog box in Figure 20.3 appears. Functions for right mouse button ┌─────────────── Right Mouse ──────────┼─────┐ │ │ │ │ On right mouse button click: │ │ │ ──┐ │ │ │ (∙) Context-sensitive Help │ │ │ │ ├─┘ │ │ ( ) Execute up to this line │ │ │ ──┘ │ ├────────────────────────────────────────────┤ │ < OK > < Cancel > < Help > │ └────────────────────────────────────────────┘ Figure 20.3 Right Mouse Dialog Box The Right Mouse dialog box lets you select one of two functions for the right mouse button: ■ Invoking on-line help (same function as the Topic command on the Help menu). This is the default setting. ■ Executing the program from the beginning of the program to the current cursor location. Both functions have advantages in different situations. You may find the Help function more useful when you are writing your program, especially if you are new to QuickBASIC. During debugging, you may find the execution feature more valuable. If you use the Context-sensitive Help option, remember that the subject of the help is the word containing the cursor. 20.4 Syntax Checking Command(Full Menus Only) The Syntax Checking command on the Options menu toggles automatic syntax checking on and off. QuickBASIC defaults to the "on" setting, indicated by a bullet (■) next to the command. To turn syntax checking off, choose the Syntax Checking command; the bullet disappears. QuickBASIC records your options when you quit. If you exit QuickBASIC with syntax-checking off, it will remain off the next time you start QuickBASIC. When on, this feature checks the syntax of each line when it is entered. See Also Section 12.5.2, "Automatic Syntax Checking" 20.5 Full Menus Command The Full Menus command toggles QuickBASIC's extended menus on and off. When Full Menus is toggled on, a bullet (■) appears next to the command. You can use QuickBASIC's menus in either their "easy" or "full" form. In their easy form, the menus contain all of the functions necessary to create beginning to intermediate-level programs. Some advanced features do not appear under Easy Menus in order to simplify the use of the environment for programmers new to QuickBASIC. Full Menus include an additional item (the Calls menu) and more commands under each of the other menus. Once you are comfortable with QuickBASIC and need advanced features, use the Full Menus option. When you exit, QuickBASIC saves all of the options you have selected, including Display options, Search Paths, Syntax Checking, and Full Menus. When you next return to QuickBASIC your choices will still be active. ──────────────────────────────────────────────────────────────────────────── Chapter 21 The Help Menu Choosing commands on the Help menu is one way to access QuickBASIC's on-line help. (For information on other methods of accessing on-line help, see Section 10.8, "Using Help.") The Help menu contains the following commands: ■ Index. Displays an alphabetical list of QuickBASIC keywords and a brief description of each. ■ Contents. Displays a visual outline of the on-line help contents. ■ Topic. Provides syntax and usage information on specific variables and QuickBASIC keywords. ■ Help On Help. Describes how to use on-line help and common keyboard shortcuts. 21.1 Index Command The Index command displays an alphabetical list of the QuickBASIC keywords. To receive information on a particular keyword, move the cursor to the line containing that keyword and press F1. QuickBASIC displays the Help window for that keyword. You can scroll through the keyword list or jump directly to a specific letter in the list. For example, if you type G, QuickBASIC moves the cursor to GET, the first keyword beginning with the letter "G." See Figure 21.1. ┌──────────────── HELP: QuickBASIC Language Keyword Index ────────────┤├── │ ╔═══╗ │═══════════════════════════════════════════════════════════════╣ G ║ │ ╚═══╝ │ GET Statement │ GOSUB Statement │ GOTO Statement │ ╔═══╗ ╞═══════════════════════════════════════════════════════════════╣ H ║ │ ╚═══╝ │ HEX$ Function │ ╔═══╗ ╞═══════════════════════════════════════════════════════════════╣ I ║ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ Figure 21.1 Index Entries for Help See Also Section 21.3, "Topic Command" 21.2 Contents Command The Contents command displays a table of contents for on-line help. It provides hints on using the QuickBASIC environment and the BASIC language, along with useful tables. From here you can transfer to the subject that interests you. See Figure 21.2. File Edit View Search Run Debug Calls Options Help ┌──────────────────────── HELP: Table of Contents ────────────────────┤├── │ Help on Help Contents Index Product Support Copyright │────────────────────────────────────────────────────────────────────────── │Using QuickBASIC BASIC Programming Language │ │ Shortcut Key Summary Functional Keyword Lists │ Edit Keys Syntax Notation Conventions │ View Keys │ Search Keys Fundamental Building Blocks │ Run and Debug Keys Data Types │ Help Keys Expressions and Operators │ Modules and Procedures │ Limits to QuickBASIC Programs │ VErsion 4.5 Differences │ ASCII Character Codes │ Survival Guide Keyboard Scan Codes │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ Figure 21.2 Table of Contents for Help For detailed information on a particular topic, place your cursor on the topic and press F1. QuickBASIC displays on-line help on that topic. For example, the Table of Contents window shows several entries under "Using QuickBASIC." If you move the cursor to "Editing keys" and press F1, a screen appears with the most frequently used editing shortcut keys. 21.3 Topic Command The Topic command provides specific information on the syntax and usage of the QuickBASIC variable, symbol, keyword, menu, command, or dialog box at or containing the cursor. When the Topic command is active, the subject on which it will provide on-line help appears after the word Topic. Choosing the Topic command is the same as pressing F1. You can get help on any keyword or variable at any time by typing the word or name and immediately choosing the Topic command. If you choose the Topic command whenever you encounter a syntax error, you can immediately correct the usage of your statement. For example, suppose you enter the line below, which is missing the word TO and instead contains a comma: FOR i% = 1,10 QuickBASIC flags the syntax error with the message Expected: TO. Press F1 or the Help button for help on the error itself. For information on the keyword FOR, move the cursor to the FOR statement and choose the Topic command. QuickBASIC keeps your program code visible at the bottom of the screen. See Figure 21.3. File Edit View Search Run Debug Calls Options Help ┌───────────────── HELP: FOR...NEXT Statement QuickSCREEN ────────────┤├── │ QuickSCREEN Detail Example Contents Index │────────────────────────────────────────────────────────────────────────── │FOR...NEXT - a control flow statement that repeats a block of │ statements a specified number of times │Syntax │ FOR counter = start TO and [STEP increment] │ [statements] │ NEXT [counter [,counter...]] │ │ ■ counter is a numeric variable used as the loop counter │ ■ start is the initial value and end is the final value of the counter │ ■ increment is the amount the counter is incremented each time │ through the loop │ │See Also EXIT FOR DO...LOOP WHILE...WEND │ ├──────────────────────────────── Untitled ───────────────────────────┤├── │FOR i% = 1,10 │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ├─────────────────────────────── Immediate ──────────────────────────────── │ │ <Shift+F1=Help> <F6=Window> <F2=Subs> <F5=Run> <F8=Step> C 00001:003 Figure 21.3 Help on the FOR...NEXT Statement To copy sample code from the FOR help screen into your program, do the following: 1. Choose the Example hyperlink at the top of the window. 2. Select the example code and choose Copy from the Edit menu. 3. Press ESC to close the Help window. 4. Move the cursor to the place in your program you want the text to appear, and choose Paste from the Edit menu. You can customize the pasted code or use it as it is. Shortcut Key F1 21.4 Help On Help Command The Help on Help command describes how to use the QuickBASIC on-line help system. The Help on Help screen gives a description of the main help features. For more specific information, press ESC to exit Help on Help, and use the Topic command on the Help menu or press F1. File Edit View Search Run Debug Calls Options Help ┌─────────────────────────── HELP: Help on Help ──────────────────────┤├── │ Help on Help Contents Index Product Support │────────────────────────────────────────────────────────────────────────── │ Use Help as follows: │ │ ■ To get help anytime, press F1 or click the right mouse button. │ ■ To get help on any part of a BASIC statement, a QuickBASIC menu item │ or dialog box, position the cursor there press F1. │ ■ To remove the help information from the screen, press ESC. │ ■ To scroll help information, press PGDN. │ │ Look for the help display in either │ ■ The Help window at the top of the screen │ ■ A dialog box which pops up in the center of the screen │ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ Figure 21.4 Help on Help Screen Shortcut Key SHIFT+F1 ──────────────────────────────────────────────────────────────────────────── Glossary The purpose of this glossary is to define unique terms used in all the manuals that accompany QuickBASIC Version 4.5. Neither the individual definitions nor the list of terms is intended to be a comprehensive dictionary of computer-science terminology. 8087, 80287, or 80387 coprocessor Intel(R) hardware products dedicated to very fast number processing. absolute coordinates Horizontal and vertical distances from the screen's upper-left corner, which has the coordinates (0,0). Absolute coordinates are measured in pixels. See also "physical coordinates." address A location in memory. algorithm A step-by-step procedure for solving a problem or computing a result. animation A QuickBASIC debugging feature in which each line in a running program is highlighted as it executes. The Trace On command from the Debug menu turns on animation. argument A data item supplied to a BASIC statement, function, procedure, or program. In the following example, the string "Hello" is an argument to the BASIC statement PRINT: "Hello". An argument may be a constant or a variable. Arguments are often used to pass information from one part of a program to another. Use the COMMAND$ function to make DOS command line arguments available to the programs. arithmetic conversion Converting numbers between integral and floating-point types. array A sequentially numbered set of elements with the same type. array bounds The upper and lower limits of the dimensions of an array. ASCII (American Standard Code for Information Interchange) A set of 256 codes that many computers use to represent letters, digits, special characters, and other symbols. Only the first 128 of these codes are standardized; the remaining 128 are special characters that are defined by the computer manufacturer. aspect ratio The ratio of a video screen's width to its height. This term is also frequently used to describe pixels. If you think of a pixel as being rectangular, its aspect ratio would be the ratio of its width to height. A typical IBM PC display has an aspect ratio of about 4:3. assignment The process of transferring a value to a variable name. The statement X = 3 assigns x a value of 3. attributes Color, intensity, blinking, and other displayed characteristics of characters or pixels. automatic variable A variable in a SUB or FUNCTION procedure whose value is not saved between invocations of the procedure. Automatic variables are frequently used in recursive procedures where you do not want values saved between calls. base name The part of a file name before the extension. For example, SAMPLE is the base name of the file SAMPLE.BAS. binary A mathematical term referring to the base-two numbering system, which uses only two digits: 0 and 1. binary file In input/output operations, files or data that contain nonprinting characters as well as ordinary ASCII characters. Binary file access is the ability to access any byte within a file, treating it as a numeric value rather than as text. BIOS (Basic Input/Output System) Machine-language programs built into a computer. These programs provide the lowest level of operations in a computer system. You can use the BIOS programs directly with the INTERRUPT and CALL INTERRUPTX statements. bit The smallest unit of information used with computers; corresponds to a binary digit (either 0 or 1). Eight bits make up one byte. block A sequence of declarations, definitions, and statements. breakpoint A specified location where program execution will halt during debugging. See "watchpoint" for a description of variable breakpoints. byte The unit of measure used for computer memory and data storage. One byte contains eight bits and can store one character (a letter, number, punctuation mark, or other symbol). call by reference See "pass by reference." call by value See "pass by value." CGA (Color Graphics Adapter) A video adapter capable of displaying text characters or graphics pixels. Color can also be displayed with the appropriate display monitor. character string A group of characters enclosed in quotation marks ( " " ). check box A pair of brackets on a QuickBASIC dialog box where you turn an option on or off. An X appears in the box when the option is on. choose To carry out a command by performing an action such as using a command button from a dialog box or an item from a menu. click To press and release one of the mouse buttons (usually while pointing the mouse cursor at an object on the screen). Clipboard A storage area that holds copied or cut text. Text does not accumulate in the Clipboard: new text added to the Clipboard replaces any text that was already there. You can use the Paste command to insert text from the Clipboard into a file. communications port See "port." compile To translate statements into a form that the computer can execute. compiler A program that translates statements into a language understood by the computer. constant A value that does not change during program execution. current directory The directory in which DOS looks for files unless otherwise instructed. current drive The drive containing the disk on which DOS looks for a directory or file unless otherwise instructed. cursor The blinking line or box on the screen. The cursor indicates the current location where text from the keyboard will appear. data The numbers and text processed by a computer in doing its work. data file A file that contains the data used or generated by a program; data can be numbers, text, or a combination of the two. debugger A program that helps to locate the source of problems discovered during run-time testing of a program. declaration A construct that associates the name and characteristics of a variable, function, or type. DEF FN function The object defined by a single-line DEF FN statement or by a DEF FN...END DEF block. (A FUNCTION procedure is generally preferred to a DEF FN function because a procedure is more portable and modular.) default A setting that is assumed unless you specify otherwise. default data type The type that BASIC uses for data unless you use a DEFtype statement to specify otherwise. The default type for numeric data is single precision. DEFtype A name used in these manuals for the group of BASIC statements that redefine a program's default variable type (DEFDBL, DEFINT, DEFLNG, DEFSNG, DEFSTR). device A piece of computer equipment, such as a display or a printer, that performs a specific task. device name The name by which DOS refers to a device (for example, PRN, LPT1, LPT2, or LPT3 for a printer). Device names are treated like file names by DOS. dialog box A box that appears when you choose a menu command that requires additional information. dimension The number of subscripts required to specify a single array element. For instance, the statement DIM A$(4,12) declares a two-dimensional array, while DIM B$(16,4,4) declares a three-dimensional array. DIRECTION keys A set of keys, found on many computer keyboards, that move the cursor left, right, up, or down on the screen. These keys usually have arrows on their key tops. directory The index of files that DOS maintains on a disk. document A way of classifying a file as text when you load it into the QuickBASIC editor. Loading a file as a document turns off syntax checking, capitalization of keywords, and other smart-editor features. You can load a BASIC program as a document if you want to edit it as you would with a word processor. double click To press the mouse button twice quickly (usually while pointing the mouse cursor at an object on the screen). double precision A real (floating-point) value that occupies eight bytes of memory. Double-precision values are accurate to 15 or 16 digits. drag Pointing the mouse cursor at an object on the screen and pressing a mouse button, then moving the mouse while holding the button down. The object moves in the direction of the mouse movement. When the item is where you want it, release the button. dynamic array An array whose memory location is allocated when the program runs. The locations are not predetermined and can change during the course of program execution. EGA (Enhanced Graphics Adapter) A video adapter capable of displaying in all the modes of the color graphics adapter (CGA) and many additional modes. The EGA supports both text and graphics at medium resolution in up to 64 colors. emulator A floating-point math package that uses software to perform the same operations as a hardware math coprocessor. enabled event An event for which QuickBASIC actively checks. Events are enabled by the ON event statements. event An action the computer can be programmed to detect. Events include items such as mouse clicks, menu selections, keyboard activity, and time passage. event trapping To detect and respond to events, for example, to branch to an appropriate routine. executable file A file with the extension .EXE, .COM, or .BAT. Executable files can be run by typing the file name at the DOS prompt. execute To run a program or carry out a specific statement in the Immediate window. exponentiation The raising of a number x to a power y; the number x is multiplied by itself y times. For example, 2^3 is 2 * 2 * 2, or 2 raised to the power of 3. expression A combination of operands and operators that yields a single value. extension The part of a file name following the period. For example, .DAT is the extension in the file name TEST.DAT. far address A memory location specified by using a segment (a location of a 64K block) and an offset from the beginning of the segment. Far addresses require four bytes──two for the segment, and two for the offset. A far address is also known as a segmented address. file buffer An area in memory in which temporary data are stored. QuickBASIC keeps a copy of the file in a buffer and changes it as you edit. This buffer is copied to disk when you save the file. filespec The complete specification of a file. The filespec can include a drive letter, path name, file name, and extension. flags register A register containing information about the status of the central processing unit and the last operation performed. floating point Notation, similar to scientific notation, that is a convenient method for expressing very large numbers, very small numbers, or numbers with fractions. A floating-point number has two parts: an exponent and a fractional part known as the mantissa. See "IEEE format." formal parameters Variables that receive the arguments passed to a function or subprogram. See "parameter." FUNCTION A block of statements beginning with FUNCTION and ending with END FUNCTIONthat defines a procedure. FUNCTION procedures can be used instead of the DEF FN functions used in older forms of BASIC. function declaration A declaration that establishes the name and type of a function. The function itself is defined explicitly elsewhere in the program. function definition A statement block that specifies a function's name, its formal parameters, and the declarations and statements that define what it does (i.e., carry out the function). global constant A constant available throughout a program. Symbolic constants defined in the module-level code are global constants. global symbol A symbol available throughout a program. Function names are always global symbols. See also "symbol" and "local symbol." global variable A variable available throughout a program. Global variables can be declared in COMMON, DIM, or REDIM statements by using the SHARED attribute. heap An area of random-access memory used by BASIC to store, among other things, variables and arrays. hexadecimal The base-16 numbering system whose digits are 0 through F (the letters A through F represent the digits 10 through 15). Hexadecimal numbers are often used in computer programming because they are easily converted to and from binary, the base-2 numbering system the computer itself uses. highlight A reverse-video area in a text box, window, or menu marking the current command chosen or the text that has been selected for copying or deleting. hyperlink A link between two related pieces of information. Hyperlinks appear between two triangles in help screens. I/O redirection See "redirect." IEEE format An international standard method of representing floating-point numbers in the computer's hardware. IEEE format gives more accurate results than the Microsoft Binary format used in earlier versions of QuickBASIC and makes it easier to use a math coprocessor. The acronym IEEE stands for Institute of Electrical and Electronics Engineers, the organization that developed this standard. See "floating point." Immediate window The area at the bottom of the QuickBASIC screen used to enter statements and execute them immediately. include file A text file that is translated into a program with the $INCLUDE metacommand. input/output (I/O) A term that refers to the devices and processes involved in the computer's reading (input) and writing (output) data. input The data that a program reads. insert mode A mode for inputting data to the QuickBASIC environment. In this mode, you can insert new characters rather than replace characters already in the file as they are entered. integer A whole number represented inside the machine as a 16-bit two's complement binary number. An integer has a range of -32,768 to +32,767. See "long integer." interface The boundary between two systems or entities, such as a disk drive and the computer, or the user and a program. interpreter A program that translates and executes one BASIC statement at a time. An interpreter translates a statement every time it executes the statement. BASICA is a language interpreter. By comparison, a compiler translates all statements prior to executing any. keyword The name of a BASIC statement, function, or operator. Examples of keywords are MOD, OPEN, OR, PRINT, and SIN. label An identifying string that marks, precedes, or denotes a specific location in a program. Labels are used by GOTO statements. link To resolve references among the modules in a program and from the program to library routines. The link step results in a complete program ready for execution. list box A box that lists a series of items. For example, the box that lists files in the Open Program dialog box is a list box. See also "dialog box." local constant A constant whose scope is limited to a particular unit of code, such as the module-level code, or a procedure within a module. All constants defined in CONST statements inside a procedure are local constants. See "global constant." local symbol A symbol that has value only within a particular function. A function argument or a variable declared as static within a function can be a local symbol. See also "global symbol." local variable A variable whose scope is confined to a particular unit of code, such as the module-level code, or a procedure within a module. All variables in a procedure are local unless they appear in a SHARED statement within the procedure, or in a COMMON SHARED, DIM SHARED, or REDIM SHARED statement at the module level of the module containing the procedure definition. See "global constant." logical device A symbolic name for a device that the user can cause to be mapped to any physical (actual) device. long integer A whole number represented inside the machine by a 32-bit two's complement value. Long integers have a range of -2,147,483,648 to +2,147,483,647. See "integer." LPT1, LPT2, LPT3 Abbreviations for line printer. The names refer to the three ports to which parallel printers can be attached. main module The module containing the first executable statement (the program's entry point). See "module." math coprocessor An optional hardware component, such as an 8087, 80287, or 80387 chip, that improves the speed of floating-point arithmetic. QuickBASIC automatically takes advantage of a math coprocessor if it is present, or emulates it in software if it is not. See "floating point." MCGA (Multicolor Graphics Array) A printed-circuit card that controls the display. The MCGA card, located in the system unit of a computer, shows both text and graphics at low to medium resolution in up to 256 colors. MDA (Monochrome Display Adapter) A printed-circuit card that controls the display. The MDA shows text only at medium resolution in one color. menu bar The bar at the top of the QuickBASIC display containing the menu titles. metacommands Special commands, enclosed in comments in a source file, that tell the compiler to take certain actions while it is compiling the program. For example, the $INCLUDE metacommand tells the compiler to translate statements found in a specified file. See "include file." Microsoft Binary format A method of representing floating-point numbers internally. Microsoft Binary format is used by versions of QuickBASIC prior to Version 3.0. See "floating point" and "IEEE format." modular programming An approach to programming in which the program is divided into functional blocks, each performing a specific task. module A section of program code that is stored in a separate file and can be separately compiled. Every program has at least one module (the main module). module-level code Program statements within any module that are outside a FUNCTION or SUB definition. Error- or event-handling code and declarative statements such asCOMMON, DECLARE, and TYPE can appear only at the module level. mouse A pointing device that fits under your hand and rolls in any direction on a flat surface. By moving the mouse, you move the mouse cursor in a corresponding direction on the screen. mouse cursor The reverse-video rectangle that moves to indicate the current position of the mouse. The mouse cursor appears only if a mouse is installed. multidimensional array An array of with more than one subscript, for example, x(5,35). A multidimensional array is sometimes referred to as an array of arrays. near address A memory location specified by using only the offset from the start of the segment. A near address requires only two bytes of memory. See also "far address." null character The ASCII character encoded as the value 0. object file A file (with the extension .OBJ) containing relocatable machine code produced by compiling a program and used by the linker to generate an executable file. offset The number of bytes from the beginning of a segment in memory to a particular byte in that segment. operand A constant or variable value that is manipulated in an expression. operator One or more symbols that specify how the operand or operands of an expression are manipulated. output The result of a program's processing, usually based on some form of input data. output screen The screen where output appears when you run a program in the QuickBASIC environment. The output screen is the same as it would be if you ran the debugged program outside of QuickBASIC. overflow An error condition that occurs when the value assigned to a numeric variable falls outside the allowable range for that variable's type. overlay Part of a program that is read into memory from disk only if and when it is needed. palette The displayable colors for a given video mode. The CGA mode operates with a set of predetermined palette colors. The EGA, MCGA, and VGA color modes operate with a redefinable palette of colors. parallel port The port to which the printer is usually attached. parameter A variable symbol in a DEF FN, FUNCTION, or SUB statement. Parameters are replaced by actual variables and values when you invoke the function or subprogram. pass by reference To transfer the address of an argument to a SUB or FUNCTION. Passing by reference allows a procedure to change the values of arguments passed to it. pass by value To transfer the value (rather than the address) of an argument to a SUB or FUNCTION. path name The complete specification that gives the location of a file. A path name usually includes a drive letter followed by a colon, one or more directory names, and a file name. physical coordinates The screen coordinates. The physical coordinates (0,0) refer to the upper-left corner of the screen, unless you have defined a graphics viewport with a VIEW statement, in which case (0,0) are the coordinates of the upper-left corner of the viewport. The range of the physical coordinates depends on the display adapter, the monitor, and the specifications set by the SCREEN statement. Units are pixels. See also "absolute coordinates" and "view coordinates." place marker A location in the program code to which you can return by pressing a control code. pointer See "mouse cursor." port An electrical connection through which the computer sends and receives data to and from devices or other computers. precedence The relative position of an operator in the hierarchy that determines the order in which expressions are evaluated. procedure A general term for a SUB or FUNCTION. See "FUNCTION" and "SUB." procedure call A call to a SUB or FUNCTION. program One or more modules linked together to form a complete set of executable instructions. program step To highlight and execute the next instruction. prompt A request displayed by the computer for you to provide some information or perform an action. QB Advisor The detailed, context-sensitive on-line help on the BASIC language. Quick library A file produced with the Make Library command or with the /Q option of the LINK command. A Quick library contains procedures for use in the QuickBASIC environment as the program is developed. Quick libraries were known in previous versions of QuickBASIC as user libraries; however, user libraries cannot be used as Quick libraries, and vice versa. random-access file A file that can be read or written in any order. See "sequential file." read-only file A file whose read-only attribute is set so that its contents can be displayed and read, but not changed. record A series of fields treated as a meaningful unit in a data file or a variable declared as having a user-defined type. See "user-defined type." recursion The practice of having a subprogram call itself; some algorithms can be coded quickly and efficiently by using recursion. redirect To specify a device (other than the default device) from which a program will receive input or to which it will send output. Normally program input comes from the keyboard, and program output goes to the screen. reference bar The line on the bottom of the QuickBASIC environment screen containing frequently used commands and keyboard shortcuts. relational database A database in which any field or record can be associated with any other field or record. registers Areas in the processor where data can be temporarily stored during machine-level processing. The registers used in the 8086-family of processors are: AX, BX, CX, DX, SP, BP, SI, DI, DS, ES, SS, CS, IP, and the flags register. See "flags register." root directory The main directory that DOS creates on each disk. The root directory is the top directory in a hierarchical file system. run time The time during which a program is executing. Run time refers to the execution time of a program, rather than to the execution time of the compiler or the linker. Some errors──known as run-time errors──can be detected only while the program is running. run-time library A file containing the routines required to implement certain language functions. run-time module A module containing most of the routines needed to implement a language. In QuickBASIC, the run-time module is an executable file named BRUN45.EXE and is, for the most part, a library of routines. scope The range of statements over which a variable or constant is defined. See "global constant," "global variable," "local constant," and "local variable." scroll To move text up and down, or left and right, to see parts that cannot fit within a single screen. scroll bars The bars that appear at the right side and bottom of the View window and some list boxes. Scroll bars allow you to scroll the contents of a View window or text box with the mouse. segment An area of memory, less than or equal to 64K, containing code or data. select To pick items, such as option buttons, in a dialog box. This verb also describes the action of highlighting areas of text or graphics to edit. sequential file A file that can be read or written only in order from first byte to last. See "random-access file." serial port The communications port (COM1, COM2, COM3, or COM4) to which devices, such as a modem or a serial printer, can be attached. simple variable A BASIC variable that is not an array. Simple variables can be of numeric, string, or user-defined types. single precision A real (floating-point) value that occupies four bytes of memory. Single-precision values are accurate to seven decimal places. smart editor Collective term for QuickBASIC's advanced editing features, including syntax checking, automatic keyword capitalization, and automatic procedure declaration. source file A text file containing BASIC statements. Although all modules are source files, not all source files are modules (include files, for example). QuickBASIC uses source files in two different formats. Source files saved in the QuickBASIC format load quickly but cannot be directly read or manipulated by an ordinary text editor. Source files saved as text files (ASCII files) can be read or changed by any text editor. stack An area of random-access memory used by BASIC to store data (e.g., information), such as intermediate results of some arithmetic computations, automatic variables in procedures, and procedure invocation information. stand-alone file An executable file that can be run without a run-time file──a compiled program linked with BCOM45.LIB. standard input The device from which a program reads its input unless the input is redirected. In normal DOS operation, standard input is the keyboard. standard output The device to which a program sends its output unless redirected. In normal DOS operation, standard output is the display. statement A combination of one or more BASIC keywords, variables, and operators that the compiler or interpreter treats as a single unit. A BASIC statement can stand by itself on a single program line. The term statement refers to one-line statements such as OPEN or INPUT as well as entire multiline compound statements such as IF...END IF or SELECT CASE...END SELECT. Parts of compound statements such as ELSE or CASE are referred to as clauses. static array An array whose memory location is allocated when the program is compiled. The memory location of a static array does not change while the program runs. stop bit A signal used in serial communications that marks the end of a character. string A sequence of characters, often identified by a symbolic name. In this example, Hello is a string: PRINT "Hello". A string may be a constant or a variable. SUB A unit of code delimited by the SUB and END SUB statements. A SUB (usually called a SUB procedure) provides an alternative to the older BASIC GOSUB type of subroutine. subprogram See "SUB." subroutine A unit of BASIC code terminated by the RETURN statement. Program control is transferred to a subroutine with a GOSUB statement. (Also called a GOSUBblock.) symbol A name that identifies a location in memory. symbolic constant A constant represented by a symbol rather than the literal constant itself. Symbolic constants are defined using the CONST statement. text Ordinary, printable characters, including the uppercase and lowercase letters of the alphabet, the numerals 0 through 9, and punctuation marks. text box A box in which you type information needed to carry out a command. A text box appears within a dialog box. text editor A program that you use to create or change text files. text file A file containing text only. tiling The filling of a figure with a pattern (instead of a solid color) by using the graphics statement PAINT. title bar A bar, located at the top of a View window, that shows the name of the text file or module (and procedure, if appropriate) currently displayed in that window. toggle A function key or menu selection that turns a feature off, if it is on, or turns the feature on, if it is off. When used as a verb, toggle means to reverse the status of a feature. For example, the Trace On command on the Debug menu toggles tracing on or off. two's complement A type of base-2 notation used to represent positive and negative in which negative values are formed by complementing all bits and adding 1 to the results. type The numeric format of a variable. Types include integer, long integer, single precision, and double precision. Types may also be user-defined. type checking An operation in which the compiler verifies that the operands of an operator are valid or that the actual arguments in a function call are of the same types as the corresponding formal parameters in the function definition. type declaration A declaration that defines variable names as members of a particular data structure or type. underflow An error condition caused when a calculation produces a result too small for the computer to handle internally. unresolved external A procedure declared in one module, but not defined in another module that is linked with it. Unresolved external references are usually caused by misspellings or by omitting the name of the module containing the procedure from the LINK command line. user-defined type A composite data structure that can contain both string and numeric variables (similar to a C-language structure or Pascal record). User-defined types are defined with TYPE statements. The data structure is defined by a TYPE...END TYPE statement. variable A value that can──and usually does──change during program execution. view coordinates Pairs of numbers (for example, x and y) that uniquely define any point in two-dimensional space. The numbers x and y can be any real numbers. View coordinates can be mapped to the screen with the graphics WINDOW statement. View coordinates let you plot data using coordinates appropriate to the graph or picture without worrying about the actual screen coordinates. See "physical coordinates." View window The main editing window and the window into which programs load. VGA (Video Graphics Array) A printed-circuit card that controls the display. A VGA card shows both text and graphics at medium to high resolution in up to 256 colors. Watch window A window that displays information about variables or expressions that you are monitoring during program execution. For each watched item, the Watch window displays the item's originating location, its name, and its current value if the item is watchable. watchable A debugging term that describes whether a variable or expression can be watched in the current execution location. An item is watchable only during execution of the part of the program from which you entered the item in the Watch window. watchpoint An expression (such as X = 3) that stops program execution when it becomes true. Watchpoints can slow program execution. See "breakpoint." wild card One of the DOS characters (? and *) that can be expanded into one or more characters in file-name references. window An area on the screen used to display part of a file or to enter statements. Window refers only to the area on the screen, and does not refer to what is displayed in the area. The term window also refers to the portion of a view coordinate system mapped to the physical coordinates by the WINDOW graphics statement. See "Immediate window," "View window,"and "Watch window." ──────────────────────────────────────────────────────────────────────────── Index Symbols . (dot) beside command ... (ellipsis dots) with menu item Numbers 80287 80387 8087 A Absolute coordinates Active window changing changing size described line and column counters switching Add Watch command Address defined near Advisor. See QB Advisor Algorithms ALT key described ALT key dialog boxes, use in entering high-order ASCII characters menus and commands Altering text AND operator Animation Apostrophe (') Arguments Arithmetic conversion floating point overflow Array bounds checking defined Array elements, specifying Array variables Arrays defined dynamic multidimensional static Arrow keys. See DIRECTION keys ASCII characters corresponding to control sequences entering high-order set Aspect ratio Assignment Assignment statement Attributes Automatic formatting Automatic syntax checking B /B option (QB) Bar, menu Base name BASIC command-line compiler. See BC BASICA programs, running with QuickBASIC BC BCOM45.LIB BIOS Bit, defined Black-and-white monitors. See Monitors, monochrome Block Boolean expressions compound precedence of evaluation simple Branching Break on Errors command Breaking out of programs Breakpoints defined deleting described setting Breaks, checking at run time BRUN45.EXE BRUN45.LIB Buffer Bugs Buttons, right mouse Byte C /C option (QB) Calculations floating point Immediate window Call by reference. See Passing by reference Call by value. See Passing by value Calls menu Calls, procedure Canceling commands CAPS LOCK/NUM LOCK indicator illus described Case sensitivity CGA. See Color Graphics Adapter CHAIN statement Change command described dialog box, illus. Changing active window default search paths main modules programs screen display text values of variables window size Character strings Check boxes defined described illus. Checking syntax types Choosing commands Easy Menus ENTER key keyboard menus mouse defined CHR$ function Clear All Breakpoints command Clear command Clearing screens View window Clicking Clipboard Closing Help /CMD option (QB) Code module level Color Graphics Adapter (CGA), defined Colors. See Screen colors Column counter, illus. Command buttons described Example Help illus. Make EXE Make EXE and Exit Make Library and Exit Program Remarks COMMAND$ function Commands Add Watch availability Break on Errors canceling Change choosing Easy Menus ENTER key keyboard menus mouse Clear Clear All Breakpoints Contents Continue Copy Create File Cut debugging Debug menu described F10 F7 F8 F9 function keys (table) table Delete Watch Display DOS Shell editing (table) Execute to cursor Exit Find Full Menus Help Help on Help History On Include File Include Lines Index Instant Watch Label Load File Make EXE File dialog box, illus. introduction Make Library Merge New FUNCTION New Program New SUB Next Statement Next SUB Open Program Output Screen Paste Print defined dialog box, illus. Help procedure stepping QB Repeat Last Find Restart Right Mouse Save Save All Save As Selected Text Set Main Module Set Next Statement Set Paths shortcut keys single stepping Split Start starting QuickBASIC SUBs defined moving procedures Syntax Checking Toggle Breakpoint Topic Trace On Undo Unload File Comments, appearing in QCARDS COMMON statement Compile Compiler Compiler/environment differences Constants defined local symbolic Contents command Context debugging execution Context-sensitive help Continue command Continuing suspended programs Control-sequence characters Conventions, document Conversion, arithmetic Coordinates absolute physical Coprocessor Copy command Copying examples from help text Create File command Creating executable files FUNCTION procedures libraries main modules new subprograms procedures CTRL key, entering special characters CTRL+BREAK Current directory Current drives Current Statement option (Display command) Cursor defined illus. moving Customizing screen display Cut command D Data Data types, default changing defined for procedures Database Debug menu commands (list) illus. (table) Debugger defined symbolic Debugging breakpoints commands debug menu F10 F7 F8 F9 function keys Run menu context, illus. Continue command features Immediate window introduction Next Statement command procedures watch variables Watch window while writing code Debugging features (table) Decision-making Declarations defined procedures, automatic DECLARE statement, procedure declarations DEF FN function defined Watch window Default Default data types changing in procedures for procedures Default search paths DEFtype defined introduction Delete Watch command closing Watch window deleting variables Deleting breakpoints modules text, command summary variables from Watch Window Details command button Devices defined logical names Dialog boxes clearing defined illus. Merge command Print command selecting items setting options text box DIM statement Dimensions DIRECTION keys defined use with menus Directories changing from within QuickBASIC changing search paths current defined listing root Display command Division DO statement, Help, illus. Document Document conventions DO...LOOP defined terminating condition UNTIL version WHILE version DOS, returning to DOS Shell command Dots, marking command Double precision Double-click Drag Drives Duplicating text. See Copying Dynamic arrays E Easy Menus commands, choosing described vs. full windows available with Edit menu Clear command commands (list) Copy command Cut command New FUNCTION command New SUB command Syntax Checking command Undo command Editing commands (table) include files material from Help Editor automatic formatting entering text selecting text syntax checking text EGA. See Enhanced Graphics Adapter Ellipsis dots (...) with menu item Emptying View window Emulator Enabled events Enhanced Graphics Adapter (EGA) Entering special characters text Environment/compiler differences Error checking, executable files ERROR function Error messages clearing help for Errors correcting running programs run-time checking line numbers reporting locations simulating syntax, checking typing Closing menus, Esc key ESC key Event trapping defined Quick libraries Events Example code copying from Help Help hyperlinks Example command button EXE requiring BRUN45.EXE option Executable files Executable files creating defined Quick libraries stand-alone Execute option (QB) Execute to cursor command Executing all statements of procedures commands. See Choosing commands programs right mouse button suspending to cursor Exit command Exiting QuickBASIC Expressions defined simple use watch F F1 key Falsity, representation Fibonacci sequence File menu commands (list) Create File command DOS Shell command Exit command illus. Load File command Merge command Open Program command Print command Save All command Save As command Save command Unload File command Files changing default search paths data executable creating defined error checking in Quick libraries stand-alone, creating include defined finding nesting viewing and editing viewing only inserting in active window loading .MAK merging object printing QB.INI read only saving sequential source stand-alone text filespec Find command described dialog box, illus. options (table) restrictions (table) FindingSearching include files text Fixed disk based Help Flags Floating point defined Floating-point arithmetic, executable files variables Floppy disk-based Help Floppy disk-based QB Advisor Flow, programs, tracing Formal parameters Formats IEEE Microsoft binary Formatting, automatic FOR...NEXT loop Full Menus Function declarations Function definitions Function keys, debugging FUNCTION procedures creating default data type naming viewing Functions, conversion option (QB) G /G option (QB) Global symbols Global variables GOSUB statement H /H option (QB) Hard disk-based help Hardware needed for running QuickBASIC Heap Help command buttons constructing statements with context sensitive copying examples from copying syntax blocks from described editing material from error messages examples files floppy-disk system hard-disk system help with hyperlinks invoking on line keys (table) keywords command button described illus. listing with Index language missing Help files on-line outline of system place markers in printing text from QB Advisor right mouse button sample programs searching for Help files Set Paths command for files syntax trouble evoking using Help menu commands (list) Contents command Help on Help command Index command introduction Topic command Help On Help command Help on Help command Help, on-lineHelp Help window described illus. moving in Hexadecimal, defined Hierarchical filing system (HFS) Highlight High-order ASCII characters High-resolution-display option (QB) History Back History Forward History On command Hyperlinks I IEEE format IF...THEN...ELSE statement defined help, illus. syntax Immediate window calculations calling procedures from capacity changing, active window context debugging in defined described illus. limits running statements in run-time error messages run-time errors, simulating size, changing statements not supported testing programs variable values, changing Implicit links #INCLUDE metacommand Include files defined finding nesting viewing and editing viewing only Included File command Included Lines command Indentation controls Indenting program blocks text Index command described screen, illus. using Input defined standard INPUT statement Input/output (I/O), defined Insert mode defined described Inserting commands, summary text Installing QuickBASIC Instant Watch command dialog box, illus. symbol help Integer variables Integers Interface Interpreter I/OInput/output K Key combinations See also Shortcut keys cursor movement described scrolling Keyboard choosing commands from moving in Help windows Keys control (CTRL) CTRL+BREAK DIRECTION F10 F7 F8 F9 Help (table) shortcut editing commands (table) Keywords capitalization of defined help L /L option (QB) Label command Labels Language help Leaving QuickBASIC. See Quitting QuickBASIC Libraries creating Quick creating defined described non-library modules, used with run-time stand-alone, executable files line Line counter, illus. Line-number checking Lines, setting attributes Linker, BRUN45.EXE, advantage of Linking Links, implicit List boxes defined described illus. scroll bar, illus. Listing directories Load File command Loading files modules Local constants symbols variables Logical devices Logical operators Logical relations Long integers Loop counters Loop variables Loops DO FOR...NEXT LPT1 M Main modules .MAK file Make EXE and Exit command button Make EXE command button Make EXE File command, dialog box, illus. Make Library and Exit command button Make Library command Math coprocessor Math functions /MBF option (QB) MCGA. See Multicolor Graphics Array MDA. See Monochrome Display Adapter Menu bar Menu-item description, illus. Menus browsing Calls clearing closing commands, choosing Debug Easy described vs. full File commands (list) illus. Full Help opening Options Run selecting setup Merge command Metacommands defined #INCLUDE Microsoft Binary format Microsoft Overlay Linker (LINK) Modes insert overtype Modular programming Module-level code defined described Modules defined deleting existing loading and unloading main changing defined new printing run-time Monitors, monochrome use with Color Graphics Adapter Monochrome Display Adapter (MDA) Mouse compatibility with QuickBASIC cursor defined Hyper Links, using with pointer, illus. QuickBASIC, using with scrolling with setting right button Moving procedures Help windows SUBs command View window text Multicolor Graphics Array (MCGA) Multidimensional arrays Multiple-module programs N Names base device path Naming procedures Near address Nested procedures Nesting Include files New FUNCTION command New Program command New SUB command Next Statement command Next SUB command NOT operator Not watchable message Null characters NUM LOCK/CAPS LOCK indicator illus described Numeric coprocessor. See Coprocessor O Object files compiling with BC defined Offset On-line help See also Help Open Program command Opening menus programs screen, illus. Operand Operators arithmetic defined logical Option boxes, illus. Option buttons described illus. Options Menu Right Mouse command Set Paths command Options menu commands (list) Display command Full Menus command Set Paths command Syntax Checking command Options, QB command OR operator Organizing QuickBASIC files OutputPRINT statement defined program, how displayed standard Output screen defined viewing Output Screen command Outputting low-order ASCII control sequences Overflow Overlay Overtyping text P PACKING.LST Palette Parallel ports Parameters defined formal Parentheses, used to establish precedence Passing by reference Passing by value Paste command Pasting text Path names Paths, changing default search Path-specification line PGDOWN key PGUP key Physical coordinates Placemarkers defined using Pointers Ports parallel serial Precedence defined introduction Preventing bugs Print command described dialog box, illus. Help PRINT statement combining numeric expressions tabbing use Problems, software, reporting Procedure declarations, automatic Procedure stepping Procedures calling from Immediate window changing default data type creating creating FUNCTION creating SUB debugging declaring default data types defined described executing all statements of naming nested sequence of SUB View window, illus. viewing Produce Debug Code check box Produce debug code check box Program command button Program execution, right mouse button Program statements Program symbols. See Symbols Programming environment, described Programming, modular Programs BASICA, running with QuickBASIC blocks, indenting continuing continuing if suspended defined executing to cursor execution continuing suspending existing, starting exiting flow, tracing instructions multiple module new, starting output resetting variables restarting restarting at first executable statement running run-time module required with sample, on disk selecting setup stand-alone starting steps stopping execution structured suspending execution testing Prompts, defined Q QB AdvisorHelp QB command QB Express QB.INI file QCARDS program Quick libraries See also Libraries defined file naming updating previous QuickBASIC debugging features installing keywords manuals, how to use mouse use options starting QuickBASIC environment, returning to QuickBASIC, Fast Load and Save option Quick-library loading option (QB) Quitting QuickBASIC R RAM space, saving with executable files README.DOC Read-only files Records Recursion Redirection Reference bar described illus. Reference, passing by Registers Relational operators Relational statements Remote-reception buffer-size option (QB) RemovingDeleting modules text Renaming programs Repeat Last Find command Repeat previous search Repeating program statements Replacing text See also Pasting text Reserved words. See Keywords Resetting variables Restart command RETURN statement RETURN without GOSUB error, cause Right Mouse command Row/column counters /RUN option (QB) Run menu debugging commands Make EXE File command Make Library command described Set Main Module command Run time defined errors checking hint regarding reporting locations simulating Running programs debugging commands errors in new Run-time libraries defined executable files Run-time module defined programs using S Save All command Save As command described dialog box, illus. Fast Load and Save option QuickBASIC option Text option Save command Saving files .MAK files procedures Saving programs Scope Screen clearing colors, setting display, customizing displaying data on illus. QuickBASIC Screen-update-speed option (QB) Scroll arrow, illus. Scroll bars defined illus. option (Display command) setting Scroll box Scrolling defined keyboard commands keys, summary of mouse text in a window Search menu Change command commands (list) Find command Label command Repeat Last Find command Selected Text command Search Paths command Searching labels procedures text Segments SELECT CASE statement described help screen, illus. Selected Text command Selecting menus programs text cautions described editing functions removing selection summary of Sequence of procedures Sequential files Serial ports Set Main Module command Set Next Statement command Set Paths command Setting breakpoints screen attributes, currently executing lines screen colors scroll bars tab stops Setting up QuickBASIC Setup menu Setup program SHARED Shortcut keys commands described introduction (table) Simple variables Single precision Single stepping Smart editor See also Editor automatic procedure declarations defined described syntax checking Source files SPACEBAR, using in dialog boxes Special characters, methods for entering Split command Splitting windows Stack Calls menu defined Stand-alone EXE File option Stand-alone files Stand-alone libraries. See Libraries Stand-alone programs, advantages Standard input and output Start command StartingLoading programs at specific statement existing new QuickBASIC Starting QuickBASIC monitors, monochrome Statement checking. See Syntax checking Statements beginning execution from CHAIN COMMON DECLARE defined DIM DO, Help, illus. ERROR GOSUB IF...THEN...ELSE, help, illus. INPUT next to execute PRINT RETURN SELECT CASE described help screen, illus. STEP using help to construct Static arrays STEP statement Stop bits Stopping programs String variables Strings character combining defined passing to QuickBASIC Structured programming SUB procedures creating default data type defined naming viewing Subprograms creating defined Subroutines SUBS command described dialog box, illus. illus. moving procedures Subscripts, defined Suspending program execution Switching active window Symbol help Symbolic constants Symbolic debuggers Symbols defined global help local using Syntax checking errors, checking help Syntax Checking command described introduction turning off T Tab TAB key, dialog boxes, using in Tab stops, setting Testing, programs Text changing copying defined deleting editors entering finding indenting inserting moving option, Save As command overtyping pasting removing replacing searching for selecting Text boxes defined described errors, correcting illus. Text files Tiling Title bar defined described illus Toggle Breakpoint command Toggles Tokens Topic command Trace On command Tracing backwards forward introduction procedure steps program flow Tracing through Help screens Trapping events, defined Truth, representation Tutorial, how to use Two's complement Types Typing mistakes Typographic conventions U Underflow Undo command Unload File command Unloading modules Unresolved externals UNTIL keyword User-defined types Using help V Value, passing by Values, changing in running programs Variables arrays automatic default type defined deleting from Watch window displaying floating-point global help illegal assignments initialization integer local naming conventions resetting simple string types values changing current determining watch Video Graphics Array (VGA) View menu commands (list) Include File command Included Lines command Next Statement command Next SUB command Output Screen command Split command SUBs command View window clearing defined described illus. loading a program in moving procedures procedures in programming in splitting Viewing procedures W Watch expressions Watch variables, debugging Watch window closing commands debugging programs defined deleting variables from described illus. monitoring variable values placing variable into watchpoints Watchable Watching expressions, in Watch window Watchpoints WHILE keyword WIndows activating Windows active changing described available with Easy Menus defined Help described illus. moving in Immediate calculations calling procedures from capacity debugging in defined described illus. running statements in run-time errors, simulating statements not supported testing programs variable values, changing window size, changing moving between size, changing splitting View defined described illus. loading a program procedures in programming in splitting Watch closing commands debugging programs defined deleting variables from described monitoring variable values placing variable into watchpoints watch described WordStar-style command indicator, illus.