More on PERFORM

Welcome back! In our journey with COBOL so far, you've learned about simple loops using PERFORM. In this lesson, we will expand on the PERFORM statement by exploring more advanced loop constructs. Understanding these concepts will enable you to create more efficient and flexible loops, essential for handling complex tasks in your programs.

In this session, you'll delve deeper into the PERFORM statement to understand how to control loops more effectively. Specifically, you will:

• Learn how to use the PERFORM UNTIL construct.
• Understand how to increment loop counters within the loop body.
• See real-world examples to solidify your understanding.

Consider the following snippet of COBOL code:

IDENTIFICATION DIVISION.
PROGRAM-ID. PerformUntilSimpleDemo.

DATA DIVISION.
WORKING-STORAGE SECTION.
01  COUNTER         PIC 9(2) VALUE 1.

PROCEDURE DIVISION.
    PERFORM UNTIL COUNTER > 5
        DISPLAY 'Counter value: ' COUNTER
        ADD 1 TO COUNTER
    END-PERFORM
    STOP RUN.

This code demonstrates how to create a loop that continues running until a certain condition is met, in this case, until COUNTER exceeds 5. The output of the code will be:

Counter value: 01
Counter value: 02
Counter value: 03
Counter value: 04
Counter value: 05

Let's break down the code to understand its key components:

1. Initialization: The variable COUNTER starts with an initial value of 1.
2. Loop Condition: The PERFORM UNTIL statement ensures that the loop will keep executing until COUNTER becomes greater than 5.
3. Loop Body:
   • Display Statement: The current value of COUNTER is displayed.
   • Increment Operation: The value of COUNTER is incremented by 1 in each iteration. Notice that we achieve that using the ADD 1 TO COUNTER statement, which is missing the GIVING clause. This is a shorthand way of incrementing the value of COUNTER by 1.
4. Termination: Once COUNTER exceeds 5, the loop terminates, and the program stops.

Understanding each of these components will allow you to employ similar constructs in your programs, making them more efficient and easier to manage.