The Calculator and Countdown exercises
ACCEPT, DISPLAY,
PERFORM..TIMES, COMPUTE, IF
Introduction
In this exercise you will amend the IterCalc.Cbl program. This program
is a version of the example iteration program shown in the introductory
COBOL lecture. Note - use your browsers back button to
get back to this page.
Download the IterCalc.Cbl
program and save it to the \WorkArea directory on drive D:.
Load the program into the NetExpress environment.
Examining IterCalc
Compile and run the program IterCalc.Cbl. Use the Animator to step
through the program and examine the contents of the Variables/Identifiers.
Examine the program and attempt to answer the following questions:-
-
What is the maximum number of digits that the variable Num1 will hold?
-
What is the maximum number of digits that Num2 will hold?
-
What is the maximum number of digits that Result will hold?
-
If a user enters more digits than the receiving variable will hold what
happens to the number entered?
-
No validation is done on values entered by the user. Examine
the program and predict what will happen if an operator other than + or
* is entered.
Test your answers by running the program and using the Animator to follow
the flow of control through the program (Step) and to examine the contents
of the variables.
Amending IterCalc
Amend the program so that instead of doing a fixed number of calculations
(three in IterCalc.Cbl) it asks the user to enter the number of calculations
required and then executes the loop that many times.
The version of the PERFORM used in this program
has the syntax PERFORM Identifer/Literal
TIMES. That is, either an identifer or a literal can be used to
indicate how many times the loop is to be executed. The current version
of IterCalc.Cbl uses a literal. You must change it so that it uses an identifier.
When run with the same data your amended program should the produce
the results shown below. For purposes of illustration, user input
is shown enlarged and in bold.
Enter the number of calcs required :- 2
Enter First Number : 3
Enter Second Number : 3
Enter operator (+ or *) : *
Result is = 9
Enter First Number : 3
Enter Second Number : 3
Enter operator (+ or *) : +
Result is = 6
Making a new program
Amend the program again. This time create a new program called Countdown.Cbl (use
Save As from the NetExpress File menu). This program
should get the user's name from the keyboard and should then display a count-down
before displaying the name that was entered.
The program should produce results similar to those shown in the example
run below. For purposes of illustration, user input is shown enlarged
and in bold.
Enter your name :- Mike Ryan
Enter the count-down start value :- 05
Getting ready to display your name.
05
04
03
02
01
Your name is Mike Ryan
Conclusion
You may be wondering if COBOL provides some sort of counting loop, like the FOR
loop in other languages, which you could use in this exercise. COBOL does
provide such a looping structure in the form of the PERFORM..VARYING.
The format (simplified) for this version is PERFORM
VARYING counter FROM start
BY step UNTIL terminatingcondition.
Last updated : March 1998
e-mail : CSISwebeditor@ul.ie
To COBOL Exercises
Evaluation Form
Search CSIS Web Site