Loadstar 12/012.d81/comal #5

Text File | 1985-01-01 | 4.2 KB | 265 lines

COMAL corner-Part 5    by Jimmy Weiler

   THE COMAL 0.14 OPERATING SYSTEM

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PART THE THIRD: GETTING SOPHISTICATED
 WITH PROGRAM ENTRY AND DEVELOPMENT
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Command: 'SIZE'

  As you write a COMAL program, part

of memory will be filled with the

program lines you type in.  When you

RUN the program, more of memory fills

up with the variables it uses.

  When you type SIZE the computer will

tell you how many bytes of memory are

still available for program lines or

variable storage.  Free space can be

a vital consideration when you are

writing large programs.

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Command: 'AUTO'

  When you enter AUTO, you tell COMAL

to automatically supply you with line

numbers as you enter program code.

You can select the starting line

number and the increment.

  AUTO by itself supplies you with

lines starting at 0010 and increasing

by 10.

AUTO
0010 first'line
0020 second'line
0030 etcetera

  AUTO followed by a single number

will supply lines starting at that

number and incrementing by 10.

AUTO 400
0400 first'line
0410 next'line
0420 etcetera

  AUTO followed by two numbers will

supply lines starting at the first

number and incrementing by the second.

AUTO 1000,100
1000 first'line
1100 second'line
1200 and'so'on

  You can stop automatic line

numbering by moving off the line with

the cursor keys.

  Line numbers are needed to keep your

program lines in order.  COMAL,

unlike BASIC, does NOT use line

numbers as references for branching.

  Because you don't need to pay much

attention to line numbers, AUTO allows

the programmer to ignore that bit of

overhead and concentrate on the REAL

work of writing code.

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Command: 'RENUM'

  This is, of course, the COMAL

"renumber" command.  It changes the

line numbers in your entire COMAL

program.

  RENUM by itself will renumber your

program starting with 0010 and

incrementing by 10.

  RENUM followed by a number will

renumber your program so that the

first line has that number and the

other lines increment by 10.

Example:
RENUM 100

RENUM followed by two numbers will

make your program lines start with

the first number and increment by the

second.

Example:

LIST
0010 PRINT "HOME";
0020 PRINT "ON THE RANGE."
RENUM 100,50
LIST
0100 PRINT "HOME";
0150 PRINT "ON THE RANGE."

  In general, there is no reason to

renumber a COMAL program unless you

need to insert an instruction between

two lines whose line numbers differ by

one.

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Command: 'DEL'

  You remove a line or a range of

lines from a COMAL program with the

DEL command.  In BASIC you can

delete a line by merely typing its

number.  In COMAL, that line would

still exist in the program, although

its contents may be changed.

Example:

Before:
LIST
100 //
105 PRINT "THERE IS NOTHING"
110 PRINT "YOU CAN'T DO WITH"
300 PRINT "COMAL, FOR ITS"
400 PRINT "STRUCTURE IS"
500 PRINT "GOOD."

DEL 100     -- deletes line 100
DEL 110,400 -- deletes all lines from
               110 through 400
After:
LIST
105 PRINT "THERE IS NOTHING"
500 PRINT "GOOD."

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Command: 'EDIT'

  When you LIST a COMAL program, the

line numbers are set off to the side

to make it more readable.  However,

when you want to change a program

line, you want it to look all crunched

up, like BASIC.

  The EDIT command is an alternate

way to list so that lines are easier

to modifiy.  You can EDIT lines one at

a time or specify a range of lines to

EDIT.

Example:

LIST 100
0100 PRINT 'WHEN I EDIT THIS, IT WILL
     LOOK A LOT  BETTER.'

EDIT 100
0100 PRINT 'WHEN I EDIT THIS, IT WILL
LOOK A LOT  BETTER.'

  If you were to edit the first

example, the resulting code might

print something like this:

WHEN I EDIT THIS, IT WILL       LOOK A
 LOT  BETTER.

  If you edit the second example, you

can be sure that the content would

not change.

WHEN I EDIT THIS, IT WILL LOOK A LOT
BETTER.

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  This concludes our introduction to

the COMAL operating system.  Now you

are ready to start learning the COMAL

language.

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