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CEnvi Shareware Manual, Chapter 2: Cmm Language Tutorial CEnvi unregistered version 1.009 9 March 1994 CEnvi Shareware User's Manual Copyright 1993, Nombas, All Rights Reserved. Published by Nombas, P.O. Box 875, Medford, MA 02155 USA (617)391-6595 Thank you for trying this shareware version of CEnvi from Nombas, a member of the Association of Shareware Professionals (ASP). 2. The Cmm Language: Tutorial for Non-C Programmers The information in this chapter is geared toward those who are not familiar with the C programming language. C programmers should jump ahead to the next chapter: Cmm versus C. This section is an introduction to and description of the Cmm programming language. If you can write a batch, script, or macro file, or if you can remember what "y = x + 1" means from your algebra class, then you're ready to take on Cmm. Really. Cmm contains only variables, mathematics symbols (remember algebra), and these few statements: IF, ELSE, DO, WHILE, FOR, SWITCH, CASE, BREAK, DEFAULT, CONTINUE, GOTO, and RETURN. This section is an abbreviation of the Cmm Language Tutorial chapter in the CEnvi registered manual. The CEnvi registered manual goes into much more depth, has many more examples, and follows a step-by-step tutorial to create a simple text editor with CEnvi. 2.1. Your first Cmm program Before going into a description of Cmm, let's first make sure that CEnvi is working properly. With a text editor (e.g., EDIT for DOS, E for OS/2, or NOTEPAD for Windows) create the file HELLO.CMM and enter this text: // Hello.cmm: My first Cmm program Count = 1; /* Count is how many Cmm programs I've written */ printf("Hello world. This is my %dst Cmm program.\n",Count); printf("Press any key to quit..."); getch(); You have now written a Cmm program named "HELLO.CMM". Don't be concerned if you do not yet understand the HELLO.CMM program; it should become clear as Cmm is defined. Now execute this program (for DOS or OS/2 you would enter "CENVI HELLO.CMM" and for Windows you need may use the File Manager and double-click on the file name). You should get this output: Hello world. This is my 1st Cmm program. Press any key to quit... If this program will execute, then you are ready to go on to learn about Cmm. If it did not execute then consult the CEnvi installation section in the first chapter of this shareware manual. 2.2. Cmm comments Comments are used in Cmm code to explain what the code does, but the comment itself does nothing. Comments are very useful in programming. A comment takes nothing away from the execution of a program, but adds immeasurably to the readability of the source code. In Cmm, any text on a line following two slash characters (//) is considered a comment and so is ignored by the Cmm interpreter. Likewise, anything between a slash-asterisk (/*) and an asterisk-slash (*/) is a comment (this type of comment may extend over many lines). In the HELLO.CMM program there is a "//" comment on the first line and a "/* blah blah */" comment on the second line. 2.3. Cmm primary data types There are three principal data types in Cmm: *Byte: A character (e.g., 'D') or a whole number between 0 and 255, inclusive *Integer: A whole number value; this is the most common numeric data type (examples: 0, -1000, 567, 4335600) *Float: floating point numbers; any number containing a decimal point (examples: 0.567, 3.14159, -5.456e-12) Cmm determines the data type of a number by how it is used; for example, in the HELLO.CMM program the "1" in the second line is an integer because that is the default type for numbers without a decimal point. 2.3.1 Escape Sequences for Characters Certain characters are represented with a multi-character sequence beginning with a backslash (\). These are called escape sequences, and have the following meanings: \a Audible bell \b Backspace \f Formfeed \n Newline \r Carriage return \t Tab \v Vertical tab \' Single quote \" Double quote \\ Backslash character \### Octal number // ex: '\033' is escape character // ex: \0 is null character \x## Hex number // '\x1B' is escape character 2.4. Cmm Variables A Cmm variable is a symbol that may be assigned data. The assignment of data is usually performed by the equal sign (=), as in the line "Count = 1" in HELLO.CMM. After variables have been assigned, they can be treated as their data type. So, after these statements: Count = 1 // assign count as the integer 1 Count = Count + 2 // same as: Count = 1 + 2 Count would now have the value 3. 2.5. Cmm Expressions, Statements, and Blocks A Cmm "expression" or "statement" is any sequence of code that perform a computation or take an action (e.g., "Count=1", "(2+4)*3"). Cmm code is executed one statement at a time in the order it is read. A Cmm program is a series of statements executed sequentially, one at a time. Each line of HELLO.CMM, for example, follows the previous line as it is written and as it is executed. A statement usually ends in a semicolon (;) (this is required in C, and still a good idea in Cmm to improve readability). Each program statement is usually written on a separate line to make the code easy to read. Expressions may be grouped to effect the sequence of processing; expressions inside parentheses are processed first. Notice that: 4 * 7 - 5 * 3 // 28 - 14 = 13 has the same meaning, do to algebraic operator precedence, as: (4 * 7) - (5 * 3) // 28 - 15 = 13 but has a different meaning than: 4 * (7 - 5) * 3 // 4 * 2 * 3 = 8 * 3 = 24 which is still different from: 4 * (7 - (5 * 3)) // 4 * (7 - 15) = 4 * -8 = -32 A "block" is a group of statements enclosed in curly braces ({}) to show that they are all a group and so are treated as one statement. For example, HELLO.CMM may be rewritten as: // Hello.cmm: My first Cmm program Count = 1; /* Count is how many Cmm programs I've written */ printf("Hello world. This is my %dst Cmm program.\n",Count); { // this block tells the user we're done, and quits printf("Press any key to quit..."); getch(); } The indentation of statements is not necessary, but is useful for readability. 2.6. Cmm Mathematical Operators Cmm code usually contains some mathematical operations, such as adding numbers together, multiplying, dividing, etc. These are written in a natural way, such as "2 + 3" when you want to add two and three. The next few subsections define the recognized operators within the comments of sample code: 2.6.1 Basic Arithmetic // "=" assignment: sets a variable's value i = 2; // i is 2 // "+" addition: adds two numbers i = i + 3; // i is now (2+3) or 5 // "-" subtraction: subtracts a number i = i - 3; // i is now (5-3) or 2 again // "*" multiplication: i = i * 5; // i is now (2*5) or 10 // "/" division: i = i / 3; // i is now (10/3) or 3 (no remainder) // "%" remainder: remainder after division i = 10; i = i % 3; // i is now (10%3) or 1 2.6.2 Assignment Arithmetic Each of the above operators can combined with the assignment operator (=) as a shortcut. This automatically assumes that the assigned variable is the first variable in the arithmetic operation. Using assignment arithmetic operators, the above code could be simplified as follows: // "=" assignment: sets a variable's value i = 2; // i is 2 // "+=" assign addition: adds number i += 3; // i is now (2+3) or 5 // "-=" assign subtraction: subtracts a number i -= 3; // i is now (5-3) or 2 again // "*=" assign multiplication: i *= 5; // i is now (2*5) or 10 // "/=" assign divide: i /= 3; // i is now (10/3) or 3 (no remainder) // "%=" assign remainder: remainder after division i = 10; i %= i % 3; // i is now (10%3) or 1 2.6.3 Auto-Increment (++) and Auto-Decrement (--) Other arithmetic shortcuts are the auto-increment (++) and auto-decrement (--) operators. These operators add or subtract 1 (one) from the value to which they are applied. ("i++" is a shortcut for "i+=1", which is itself shortcut for "i=i+1"). These operators can be used before (prefix) or after (postfix) their variables. If used before, then the variable is altered before it is used in the statement; if used after, then the variable is altered after it is used in the statement. This is demonstrated by the following code sequence: i = 4; // i is initialized to 4 j = ++i; // j is 5, i is 5 (i was incremented before use) j = i++; // j is 5, i is 6 (i was incremented after use) j = --i; // j is 5, i is 5 (i was decremented before use) j = i--; // j is 5, i is 4 (i was decremented after use) 2.7. Cmm Arrays and Strings An "array" is a group of individual data elements. Each individual item in the array is then called an "array element". An element of an array is itself a variable, much like any other variable. Any particular element of the array is selected by specifying the element's offset in the array. This offset is an integer in square brackets ([]). For example: prime[0] = 2; prime[1] = 3; prime[2] = 5; month[0] = "January"; month[1] = "February"; month[2] = "March"; An array in Cmm does not need to be pre-defined for size or data type, as it does in other languages. Any array extends from minus infinity to plus infinity (within reasonable computer memory limits). The data type for the array is the type of the data first assigned to it. If Cmm code begins with: foo[5] = 7; foo[2] = -100; foo[-5] = 4; then foo is an array of integers and the element at index 7 is a 5, at index 2 is -100, and at index -5 is 4. "foo[5]" can be used in the code anywhere that a variable could be used. 2.7.1 Array Initialization Arrays can be initialized by initializing specific elements, as in: foo[5] = 7; foo[2] = -100; foo[-5] = 4; or by enclosing all the initial statements in curly braces, which will cause the array to start initializing at element 0, as in: foo = { 0, 0, -100, 0, 0, 7 }; 2.7.2 Strings Strings are arrays of bytes that end in the null-byte (zero). "String" is just a shorthand way to specify this array of bytes. A string is most commonly specified simply by writing text within two quote characters (e.g., "I am a string.") If this statement were present in the Cmm code: animal = "dog"; it would be identical to this statement: animal = { 'd', 'o', 'g', 0 }; and in both cases the value at animal[0] is 'd', at animal[2] is 'g', and at animal[3] is 0. Escape sequences encountered in strings will be translated into their byte value. So you'll often see strings such as "\aHello world\n" where the "\a" means to beep and the "\n" means to put a newline character at the end of the string. Cmm provides the back-quote (`), also known as known as the "back-tick" or "grave accent", as an alternative quote character to indicate that escape sequences are not to be translated. So, for example, here are two ways to describe the same file name: "c:\\autoexec.bat" // traditional method `c:\autoexec.bat` // alternative method 2.7.3 Array Arithmetic When one array is assigned to the other, as in: foo = "cat"; goo = foo; then both variables define the same array and start at the same offset 0. In this case, if foo[2] is changed then you will find that goo[2] has also been changed. Integer addition and subtraction can also be performed on arrays. Array addition or subtraction sets where the array is based. By altering the previous code segment to: foo = "cat"; goo = foo + 1; goo and foo would now be arrays containing the same data, except that now goo is based one element further, and foo[2] is now the same data as goo[1]. To demonstrate: foo = "cat"; // foo[0] is 'c', foo[1] = 'a' goo = foo + 1;// goo[0] is 'a', goo[-1] = 'c' goo[0] = 'u'; // goo[0] is 'u', foo[1] = 'u', foo is "cut" goo++; // goo[0] is 't', goo[-2] = 'c' goo[-2] = 'b' // goo[0] is 't', foo[0] = 'b', foo is "but" 2.7.4 Multi-Dimensional Arrays: Arrays of Arrays An array element is a variable, and so if the type of that element's variable is itself an array, then you have an array of arrays. A statement such as: goo[4][2] = 5; indicates that goo is an array of arrays, and that element 2 of element 4 is the integer 5. Multi-dimensional arrays might be useful for programming a tic-tac-toe game. Each row and column of the 3x3 board could be represented with a row, column element containing 'X', 'O' or ' ' (blank) depending on the character at that location. For example, a horizontal 'X' win in the middle row could be initialized like this: board[1][0] = 'X'; board[1][1] = 'X'; board[1][2] = 'X'; Note that a string is an array, and so anytime you make an array of strings you are defining an array of arrays. 2.8. Cmm Structures A "structure" is a collection of named variables that belong together as a whole. Each of the named variables in a structure is called a member of that structure and can be any data type (integer, float, array, another structure, array of structures, etc.). These structure members are associated with the structure by using a period between the structure variable and the member name. A simple and useful example of a structure is to specify a point on the screen. A point is made up of a row and column, and so you may specify: place.row = 12; // set to row 12 place.col = 20; // set at column 20 place.row--; // move up one row to row 11 Two structures can be compared for equality or inequality, and they may be assigned, but no other arithmetic operations can be performed on a structure. 2.9. printf() and getch() Although although the Cmm "function" has not yet been defined, it is useful to use two functions already, printf() and getch(), for learning more about Cmm programming. Unfortunately, printf() is about as complicated as a function can get. 2.9.1 printf() Syntax printf() prints to the screen, providing useful feedback on your programming. The basic syntax of printf() is this: printf(FormatString,data1,data2,data3,...); FormatString is the string that will be printed to the screen. When FormatString contains a percent character (%) followed by another character, then instead of printing those characters printf() will print the next data item (data1, data2, data3, etc...). The way the data will be presented is determined by the characters immediately following the percent sign (%). There are many such data formats, as described fully in the Registered User's Manual (or any C programming manual), but here's few to start with: *%% print a percentage sign *%d print a decimal integer *%X print a hexadecimal integer *%c print a character *%f print a floating-point value *%E print a floating-point value in scientific format *%s print a string There are also special characters that cause unique screen behavior when they are printed, some of which are: *\n goto beginning of next line *\t tab *\a alarm: audible beep *\r carriage-return without a line feed *\" print the quote character *\\ print a backslash Here are some example printf() statements: printf("Hello world. This is my %dst Cmm program.\n",Count); printf("%c %d %dlips",'I',8,2); printf("%d decimal is the same as %X in hexadecimal",n,n); printf("My name is: %s\n","Mary"); 2.9.2 getch() Syntax getch() (GET CHaracter) waits for any key to be pressed. The program stops executing at the getch() statement until a key is pressed. getch() is especially useful in Windows because once a program is completed its windows will go away. So getch() might be placed at the end of the program to keep the screen visible until a key is pressed. 2.9.3 Using printf() and getch() to Learn Cmm You can now experiment with what you are learning by using the printf() and getch() statements. If, during program execution, you want to know that you're about to execute an exciting piece of code, then before those interesting lines of code you may want to write: printf("Here comes the good stuff. Press any key..."); getch(); You can display values at any point in your program with a printf() statement. This short TEST.CMM program tests how "*=" works: // TEST.CMM - test the *= operator var1 = 4; var2 = 5; printf("the numbers are %d and %d\n",var1,var2); var1 *= 7; var2 *= 7; printf("after *= 7 the values are %d and %d\n",var1,var2); getch(); 2.10. Bit Operators Cmm contains many operators for operating on the binary bits in a byte or an integer. If you're not familiar with hexadecimal numbering (digits '0' to 'F'), you may want to refer to the CEnvi Registered User's Manual. i = 0x146; // "<<" shift left: shift all bits left by value // "<<=" assignment shift left i <<= 2; // shift i (0x146) left 2, so i = 0x518 // ">>" shift right: shift all bits right by value // ">>=" assignment shift right i >>= 3; // shift i (0x518) right 3, so i = 0xA3 // "&" bitwise AND // "&=" assignment bitwise and i &= 0x35; // and i (0xA3) with 0x35 so i = 0x21 // "|" bitwise OR // "|=" assignment bitwise OR i |= 0xC5; // OR i (0x21) with 0xC4 so i = 0xE5 // "^" bitwise XOR: exlusive OR // "^=" assignment bitwise XOR i ^= 0xF329 // XOR i (0xE5) with so i = 0xF3CC // "~" Bitwise complement: (turn 0 bits to 1, and 1 to 0) i = ~i; // complement i (0xF3CC) so i = 0xFFFF0C33 (OS/2) 2.11. Logical Operators and Conditional Expressions A conditional expression is evaluated to be TRUE or FALSE, where FALSE means zero, and TRUE means anything that is not FALSE (i.e., not zero). A variable or any other expression by itself can be TRUE or FALSE (i.e., non-zero or zero). With logic operators, these expressions can be combined to make encompassing TRUE/FALSE decisions. The logic operators are: * "!" NOT: opposite of decision !TRUE // FALSE !FALSE // TRUE !('D') // FALSE !(5-5) // TRUE * "&&" AND: TRUE if and only if both expressions are true TRUE && FALSE // FALSE TRUE && TRUE // TRUE 0 && (foo+2) // FALSE: (foo+2) is not evaluated !(5-5) && 4 // TRUE * "||" OR: TRUE if either expression is TRUE TRUE || FALSE // TRUE: doesn't even check FALSE TRUE || (4+2) // TRUE: (4+2) is not evaluated FALSE || (4+2) // TRUE: (4+2) is evaluated FALSE || FALSE // FALSE 0 || 0.345 // TRUE !(5-3) || 4 // TRUE * "==" EQUALITY: TRUE if both values equal, else FALSE 5 == 5 // TRUE 5 == 6 // FALSE * "!=" INEQUALITY: TRUE if both values not equal, else FALSE 5 != 5 // FALSE 5 != 6 // TRUE * "<" LESS THAN 5 < 5 // FALSE 5 < 6 // TRUE * "<" GREATER THAN 5 > 5 // FALSE 5 > 6 // FALSE 5 > -1 // TRUE * "<=" LESS THAN OR EQUAL TO 5 <= 5 // TRUE 5 <= 6 // TRUE 5 <= -1 // FALSE * ">=" GREATER THAN OR EQUAL TO 5 >= 5 // TRUE 5 >= 6 // FALSE 5 >= -1 // TRUE 2.12. Flow Decisions: Loops, Conditions, and Switches This section describes how Cmm statements can control the flow of your program. You'll notice code sections are often indented, when blocks belong together; this makes the code much easier to read. 2.12.1 IF - Execute statement (or block) if conditional expression is TRUE if ( goo < 10 ) { printf("goo is smaller than 10\n"); } 2.12.2 ELSE - Execute statement (or block) if IF block was not executed if ( goo < 10 ) { printf("goo is smaller than 10\n"); } else { printf("goo is not smaller than 10\n"); } ELSE can also be combined with IF to find one in a series of values: if ( goo < 10 ) { printf("goo is less than 10\n"); if ( goo < 0 ) { printf("goo is negative; of course it's less than 10\n"); } } else if ( goo > 10 ) { printf("goo is greater than 10\n"); } else { printf("goo is 10\n"); } 2.12.3 WHILE - Execute block while conditional expression is TRUE str = "WHO ARE YOU?"; while ( str[0] != 'A' ) { printf("%s\n",str); str++; } printf("%s\n",str); The output of the above code would be: WHO ARE YOU? HO ARE YOU? O ARE YOU? ARE YOU? ARE YOU? 2.12.4 DO ... WHILE - Execute block, and then test for conditional This is different from the WHILE statement in that the block is executed at least once, before the condition is tested. do { value++; printf("value = %d\n",value); } while( value < 100 ); The code used to demonstrate the WHILE statement might be better written this way to avoid the extra printf(): str = "WHO ARE YOU?"; do { printf("%s\n",str); } while ( str++[0] != 'A' ); 2.12.5 FOR - initialize, test conditional, then loop "for" is a combination of statements of this format: for ( initialization; conditional; loop_expression ) statement The initialization is performed first. Then the conditional is tested. If the conditional is TRUE (or if there is no conditional expression) then statement is executed, and then the loop_expression is executed, and so on back to testing the conditional. If the conditional is FALSE then the program continues beyond statement. The "for" statement is a shortcut for this form of WHILE: initialization; while ( conditional ) { statement; loop_expression; } The above code demonstrating the WHILE statement would be rewritten this way if you preferred to use the FOR statement: for ( str = "WHO ARE YOU?"; str[0] != 'A'; str++ ) printf("%s\n",str); printf("%s\n",str); 2.12.6 BREAK and CONTINUE "break" terminates the nearest loop or case statement. "continue" jumps to the test condition in the nearest DO or WHILE loop, and jumps to the loop_expression in the nearest FOR loop. 2.12.7 SWITCH, CASE, and DEFAULT The SWITCH statement follows this format: switch( switch_expression ) { case exp1: statement1 case exp2: statement2 case exp3: statement3 case exp4: statement4 case exp5: statement5 . . . default: default_statement } switch_expression is evaluated, and then it is compared to all of the case expressions (expr1, expr2, expr3, etc...) until a match is found (i.e., switch_expression == expr? ). The statements following that match are then executed until the end of the switch block is reached or until a BREAK statement exits the switch block. If no match is found, the DEFAULT: statement is executed if there is one. For example, this code handles the variable "key", which is assumed to be the value of a key that was just pressed on the keyboard: switch ( key ) { case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9: printf("A digit was pressed\n"); break; case '\r'; printf("You pressed RETURN\n"); default: printf("I am not prepared for the key you pressed\n"); break; } 2.12.8 GOTO and Labels You may jump to any location within a function block (see functions) by using the GOTO statement. The syntax is: goto LABEL; where LABEL is an identifier followed by a colon (:). if ( a < 0 ) { BadGoingsOn: // this is a label printf("\aThe value for a is very bad.\n"); abort(); // see function library for abort() } else if ( 1000 < a ) goto BadGoingsOn; GOTOs should be used sparingly, for they often make it difficult to track program flow. 2.13. Conditional Operator ?: The conditional operator is a strange-looking statement that is simply a useful shortcut. The syntax is this: test_expression ? expression_if_true : expression_if_false First, test_expression is evaluated. If test_expression is non-zero (TRUE) then expression_if_true is evaluated and the value of the entire expression replaced by the value of expression_if_true. If test_expression is FALSE, then expression_if_false is evaluated and the value of the entire expression is that of expression_if_false. For example: foo = ( 5 < 6 ) ? 100 : 200; // foo is set to 100 printf("User's name is %s\n",NULL==name ? "unknown" : name); 2.14. Functions Functions in Cmm can perform any action of any complexity, and yet they are used in statements as easily as variables. It is because of the flexibility and simplicity of functions that Cmm needs so few statements. Any action can take place in a function, and yet the function is treated by the calling code simply as the data type that the function returns. 2.14.1 Function definition A function takes a form such as this: FunctionName(Parameter1,Parameter2,Parameter3) { statements... return result; } where the function name is followed by a list of input parameters in parentheses (there can be any number of input parameters and they can be named with any variable names). A call is made to a function in this format: FunctionName(Value1,Value2,Value3) So any call to FunctionName will be result in the execution of FunctionName() with the parameters passed, and then be equivalent to whatever value FunctionName() returns. 2.14.2 Function RETURN Statement The return statement causes a function to return to the code that initially called the function. The calling code will receive the value that the function returned. Here are function examples: foo(a,b) // return a times b { return( a * b ); } foo(a,b) // return a times b { return a * b; } foo(a,b) // return the minimum value of a and b { if ( a < b ) result = a; else result = b; return(result); } foo(a,b) // return a structure with members .min and .max { // for the smaller and larger of a and b if ( a < b ) { bounds.min = a; bounds.max = b; } else { bounds.min = b; bounds.max = a; } return( bounds ); } If no value is returned, or if the end of the function block is reached without a return statement, then no value is returned and the function is a "void" type. void functions return no value to the calling code. These examples demonstrate some void-returning functions: foo(a,b) // set a = b squared. No return value. { a = b * b; return; } foo(a,b) // set a = b squared. No return value. { a = b * b; } 2.14.3 Function Example The use of functions should gain clarity with this example. This code demonstrates a function that multiplies two integers (although multiplying integers could more easily be performed with the multiply (*) operator): num1 = 4; num2 = 6; // use the standard method of multiplying numbers printf("%d times %d is %d\n",num1,num2,num1*num2); // now call our function to do the same thing printf("%d times %d is %d\n",num1,num2,Multiply(num1,num2)); // declare a function that multiplies two integers. Notice // that the integers are defined as i and j, so that's how // they'll be called in this function, no matter what they // were named in the calling code. This function will // return i added to itself j times. Multiply(i,j) { total = 0; for ( count = 0; count < j; count++ ) total += i; return(total); // caller will receive this value } When executed, the above code will print: 4 times 6 is 24 4 times 6 is 24 This example demonstrated several features of Cmm functions. Notice that in calling printf() the parameter "num1*num2" is not passed to printf, but the result of "num1*num2" is passed to printf. Likewise, "Multiply(num1,num2)" is not a parameter to printf(); instead, printf receives the return value of Multiply() as its parameter. 2.14.4 Function Recursion When a function calls itself, or calls some other function that calls itself, then it is known as a recursive function. Recursion is permitted in Cmm, as it is in C. Each call into a function is independent of any other call to that function (see section on variable scope). The following function, factor(), factors a number. Factoring is a natural candidate for recursion because it is a repetitive process where the result of one factor is then itself factored according to the same rules. factor(i) // recursive function to print all factors of i, { // and return the number of factors in i if ( 2 <= i ) { for ( test = 2; test <= i; test++ ) { if ( 0 == (i % test) ) { // found a factor, so print this factor then call // factor() recursively to find the next factor printf(" %d",test); return( 1 + factor(i/test) ); } } } // if this point was reached, then factor not found return( 0 ); } 2.15. Variable Scope A variable in Cmm is either global or local. A global variable is one that is referenced outside of any function, making it visible and accessible to all functions. A local variable is one that is only referenced inside of a function, and so it only has meaning and value within the function that declares it. Note that two local variables in different functions are not the same variable. Also, each instance of a recursive function has its own set of local variables. In other words, a variable that is not referenced outside of a function only has meaning (and that meaning is unique) while the code for that function is executing. In the following sample code, "number" is the only global variable, the two "result" variables in Quadruple() and Double() are completely independent, and the "result" variable in one call Double() is unique to each call to Double(): number = Quadruple(3); Quadruple(i) { result = Double(Double(i)); return(result); } Double(j) { result = j + j; return(result); } Note that variables that are all in uppercase letter are considered global and refer to environment variables. See the chapter on CEnvi specifics for more on environment variables. 2.16. #define "#define" is used to replace a token (a variable or a function name) with other characters. The structure is: #define token replacement This results in all subsequent occurrences of "token" to be replaced with "replacement". For example: #define HI "Hello world!" printf(HI); would result in the following output: Hello world! because HI was replaced with "Hello world!" A common use of #define is to define constant numeric or string values that might possibly change, so that in the future only the #define at the top of the file needs to be altered. For instance, if you write screen routines for a 25-line monitor, and then later decide to make it a 50-line monitor, you're better off altering #define ROW_COUNT 25 to #define ROW_COUNT 50 and using ROW_COUNT in your code (or ROW_COUNT-1, ROW_COUNT+2, ROW_COUNT/2, etc...) than if you had to search for every instance of the numbers 25, 24, 26, etc... CEnvi has a large default list of tokens that have already been #define'd, such as TRUE, FALSE, and NULL. More of these are listed in the chapter on the Internal Function Library. 2.17. #include Cmm code is executed from one stream of source code. Sometimes it is useful to break the program into different files or to access commonly used code without recreating that code again and again in every new program written. This is what "#include" is for: it allows code from another file to be included in a program. The #include syntax is: #include <Name[,Ext[,Prefix[,BeginCode[,EndCode]]]]> where: Name - Name of the file to include Ext - Extension name to add to Name if not already there Prefix - Will only include code from Name on lines that begin with this string BeginCode - Will start including code from Name following this line of text EndCode - Will stop including code when this line is read The quote characters (' or ") may be used in place of < and >. The only field that is required by Cmm is Name (this is the field used in C's #include), which is the name of the file to include. All other fields are optional, and can be left blank if unused. To include all of C:\CMM\LIB.cmm #include <c:\CMM\LIB.cmm> To include from dog.bat between the lines GOTO END and :END #include 'dog,bat,,GOTO END,:END' To include lots of little files into one big one program #include <screen.cmm> #include <keyboard.cmm> #include <init.cmm> #include <comm.cmm> In CEnvi a file will not be included more than once, and so if it has already been included, a second (or third) #include statement will have no effect. 2.18. Initialization All code that is outside of any function is part of the global initialization function. This code is executed first, before calling any function (unless a function is called from this initialization code). Any variables referenced in the initialization section are global. 2.19. main(ArgCount,ArgStrings) After the initialization has been performed, the main() function is called and is given the argument input to the Cmm program. The first parameter to main (ArgCount) is the number of arguments provided to the program. ArgStrings is an array of those input arguments, which are always strings. The first argument is always the name of the source code, or of CEnvi.exe if there is no source file. The value returned from main() should be an integer, and is the exit code (ERRORLEVEL for DOS) returned to the operating system from your program (see also exit() in the internal library). This code file TEST.CMM: printf("I am initializing\n"); main(argc,argv) { printf("This program is called %s.\n",argv[0]); printf("There are %d input arguments, as follows:\n",argc); for ( i = 0; i < argc; i++ ) printf("\t%s\n",argv[i]); return(0); } printf("still initializing\n"); When executed in this way: cenvi test.cmm I am 4 "years old" today would result in this output: I am initializing still initializing This program is called test.CMM. There are 6 input arguments, as follows: test.CMM I am 4 years old today and would return 0 to the operating system.