"Enter an integer :"to appear in the middle of the screen; and when the user enters the number and hits the ENTER key, we want to display "Even" or "Odd" accordingly just next to the entered number. To key-in the source of our program, we shall need a text editor. Actually, any editor will do. Even the Notepad utility of MS-Windows... I would recommend you to use the MS-DOS standard text editor which you can invoke with the EDIT command. Before you start creating your source file, do not forget to create your own sub-directory at a convenient place on the PC disks and change your default directory to this working space.
MKDIR \CUAYFER
CD \CUAYFER
EDIT PROG1.CBL
Please note that the file extension for our source file is CBL. This is
a convention of the RM-COBOL compiler that we shall be using and
not necessarily same for all COBOL compilers.
Since every COBOL program must have an identification division, you should
start with something like this :
IDENTIFICATION DIVISION.
PROGRAM-ID. MY-FIRST-COBOL-PROGRAM.
Please note that these lines SHOULD start on column 8. You can see the
cursor
position at the right bottom corner of the editor screen.
Please also note the "." characters, especially at the ends of the command lines.
In very near future, you shall be hunting extra and/or missing "."s in
your programs. :)
The next division we should enter is the ENVIRONMENT division :
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. ANY-MS-DOS-PC.
OBJECT-COMPUTER. ANY-MS-DOS-PC.
Please also note the dash "-" characters even in commentary fields
(MY-FIRST-COBOL-PROGRAM, ANY-MS-DOS-PC). Although some compilers will let you
use blanks in these fields; RM-COBOL won't!
Since we shall not be using any disk/tape files and/or Printers in our program,
we do not need to have an INPUT-OUTPUT SECTION. Although we shall be
using Input-Output statements, we do not need any special declarations for the
CONSOLE CRT SCREEN I/O.
Next, the DATA DIVISON! Since we shall not use any disk/tape files or printers,
we need not use a FILE SECTION. Therefore we proceed right next to the WORKING-STORAGE SECTION.
In the working-storage section, we have to declare all memory variables that
we shall use in our program. Normally, you wouldn't know all the variables
and their types that you will use in the pgm. While you are writing your code,
whenever you mention a new variable, you must come back to this section and declare it!
For our simple program, we can decide NOW that we should use at least
two emory variables; one for the number that user will enter and the other
for the remainder when we divide this number by two.
Lets choose the variable names NUMBER-ENTERED and REMNANT for the remainder.
The variable name REMAINDER would not be a good choice, BECAUSE IT IS A RESERVED WORD!.
Click here for a short list of COBOL reserved words. Please note that this is not a complete
list and further, the list will be different for various COBOL implementations.
Next, we should decide the types and length of thse variables. In this example
they certainly will be numercial; the input value can be limited to 9 digits, and REMNANT can be
be a single digit number.
The working-storage declarations for these SCALAR variables can be :
77 NUMBER-ENTERED PIC 9(9).
77 REMNANT PIC 9.
Note that the 77's start at column 8, the variable names start at column 12 or
beyond col 12!
Now are ready to proceed to PROCEDURE DIVISION. This is the part of the COBOL
code where we shall do our actual work.
All COBOL procedure divisions start with a PARAGRAPH NAME at column 8. Any name
will do but it is customary to use the name MAIN for the first paragraph. By the
way, a COBOL paragraph is a group of procedure division statements that are
collected under a common paragraph name and make some sense together with
the other statements in the paragraph. The rules related to paragraphs are very
loose except the first one.
An analogy to COBOL paragraphs are LABELS in other programming languages.
With the use of various sequence control statements (like GO TO, PERFORM), you can
branch the execution sequence to paragraphs, or in other words, to first statements
of paragraphs.
Our PROCEDURE DIVISION can go like this :
PROCEDURE DIVISION.
MAIN.
*
DISPLAY "Enter an integer :" LINE 12 POSITION 20 ERASE.
DISPLAY "Enter a zero to terminate the program" LINE 24 POSITION 20.
ACCEPT NUMBER-ENTERED LINE 12 POSITION 40.
IF NUMBER-ENTERED = ZERO THEN
DISPLAY "Normal Termination!" LINE 1 POSITION 1 ERASE
STOP RUN.
*
DIVIDE 2 INTO NUMBER-ENTERED GIVING USELESS-RESULT REMAINDER REMNANT.
Ooops! We had to introduce a new variable "USELESS-RESULT" which will hold
the quotient of division. We do need the value but the DIVIDE statement needs
it. We have to go back to working-storage section and declare it too!
The modified declaration statement group would look like :
77 NUMBER-ENTERED PIC 9(9).
77 REMNANT PIC 9.
77 USELESS-RESULT PIC 9(9).
Now back to our procedure...
PROCEDURE DIVISION.
MAIN.
*
DISPLAY "Enter an integer :" LINE 12 POSITION 20 ERASE.
DISPLAY "Enter a zero to terminate the program" LINE 24 POSITION 20.
ACCEPT NUMBER-ENTERED LINE 12 POSITION 40.
IF NUMBER-ENTERED = ZERO THEN
DISPLAY "Normal Termination!" LINE 1 POSITION 1 ERASE
STOP RUN.
*
DIVIDE 2 INTO NUMBER-ENTERED GIVING USELESS-RESULT REMAINDER REMNANT.
*
IF REMNANT = 1 THEN
DISPLAY "Odd" LINE 12 POSITION 52
ELSE
DISPLAY "Even" LINE 12 POSITION 52.
*
DISPLAY "Hit ENTER key to continue..." LINE 24 POSITION 20.
ACCEPT XDUMMY.
GO MAIN.
See? Another variable.... This time we shall add the statement
77 XDUMMY PIC X.
We shouldn't use PIC 9 for this variable because the user might enter a letter
or a special character just before hitting the ENTER key and cause trouble.
Obviously the letter "A" cannot be read into a numeric variable.
Now, the complete program should look somewhat like :
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. ANY-MS-DOS-PC.
OBJECT-COMPUTER. ANY-MS-DOS-PC.
DATA DIVISION.
WORKING-STORAGE SECTION.
77 NUMBER-ENTERED PIC 9(9).
77 REMNANT PIC 9.
77 USELESS-RESULT PIC 9(9).
77 XDUMMY PIC X.
*
PROCEDURE DIVISION.
MAIN.
*
DISPLAY "Enter an integer :" LINE 12 POSITION 20 ERASE.
DISPLAY "Enter a zero to terminate the program" LINE 24 POSITION 20.
ACCEPT NUMBER-ENTERED LINE 12 POSITION 40.
IF NUMBER-ENTERED = ZERO THEN
DISPLAY "Normal Termination!" LINE 1 POSITION 1 ERASE
STOP RUN.
*
DIVIDE 2 INTO NUMBER-ENTERED GIVING USELESS-RESULT REMAINDER REMNANT.
*
IF REMNANT = 1 THEN
DISPLAY "Odd" LINE 12 POSITION 52
ELSE
DISPLAY "Even" LINE 12 POSITION 52.
*
DISPLAY "Hit ENTER key to continue..." LINE 24 POSITION 20.
ACCEPT XDUMMY.
GO MAIN.
RMCOBOL PROG1
You do not need to specify the extension of the source file as long as
it is .CBL.
Now try it!
Too many error messages! Right?
You couldn't even follow the long list of messages... Try the MS-DOS command
RMCOBOL PROG1 | MORE
to get the long message list with a pause between screen pages.
Can you guess why you had so manu errors even in a small program like this?
Let me tell you! You typed beyond column 72 and the compiler simply ignored
all characters you typed at columns 73, 74 etc..No problem! Go back to the editor and insert new line characters into statements so that the new source looks something like :
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. ANY-MS-DOS-PC.
OBJECT-COMPUTER. ANY-MS-DOS-PC.
DATA DIVISION.
WORKING-STORAGE SECTION.
77 NUMBER-ENTERED PIC 9(9).
77 REMNANT PIC 9.
77 USELESS-RESULT PIC 9(9).
77 XDUMMY PIC X.
*
PROCEDURE DIVISION.
MAIN.
*
DISPLAY "Enter an integer :" LINE 12
POSITION 20 ERASE.
DISPLAY "Enter a zero to terminate the program"
LINE 24 POSITION 20.
ACCEPT NUMBER-ENTERED LINE 12 POSITION 40.
IF NUMBER-ENTERED = ZERO THEN
DISPLAY "Normal Termination!" LINE 1 POSITION 1 ERASE
STOP RUN.
*
DIVIDE 2 INTO NUMBER-ENTERED GIVING
USELESS-RESULT REMAINDER REMNANT.
*
IF REMNANT = 1 THEN
DISPLAY "Odd" LINE 12 POSITION 52
ELSE
DISPLAY "Even" LINE 12 POSITION 52.
*
DISPLAY "Hit ENTER key to continue..."
LINE 24 POSITION 20.
ACCEPT XDUMMY.
GO MAIN.
RUNCOBOL PROG1
What happens is this : The compiler produces a file called PROG1.COB into
your working directory and this is the "executable" (or rather "runnable")
version of your program. With the help of RUNCOBOL utility (actually is called
"COBOL RUNTIME") you "sort of execute" your program.
I use these vague terms "sort of..", "rather runnable" because unlike most compilers,
RM-COBOL does NOT translate your source into machine code! It translates
your program into an "intermediate code" and then INTERPRETS this code with the
help of its runtime; namely RUNCOBOL...
Anyway, when you run your program you should get a feeling that it is running correctly
except that the screen is a mess...
The reason is straightforward! We did not clear the screen before we started
displaying messages on the screen. Try adding the statement
DISPLAY " " LINE 1 POSITION 1 ERASE EOS.
This statement will display a blank character on the first row, first column
of the screen and then EOS (erase to end of screen).
Now, try running your program again. It looks much better now, doesn't it?
The only problem is; you cannot see the "Normal Termination..." message when
you enter a zero... Can you guess the reason? Please try to correct this defect!
It can be good quiz question! :)
Now you can play around with this program and put some fancy features in it.
For example, try to disable "beep" signal that you hear everytime a new number
is ACCEPT'ed. You can also try to make the "Hit ENTER key to continue..." message
so that it gets the user's attention.
I shall appreciate if you MAIL me the source of the revised program. All decent jokes
and funny ideas are welcome!