💻 COBOL

COBOL PERFORM and Loops

Intermediate 🕑 22 min read 👁 1 views

PERFORM Statement

PERFORM is one of the most important statements in COBOL. It's used to execute paragraphs/sections and create loops.

Types of PERFORM

Simple PERFORM - Execute a paragraph once
PERFORM TIMES - Execute a fixed number of times
PERFORM UNTIL - Execute until condition is true
PERFORM VARYING - Execute with a counter variable

PERFORM THRU

Execute a range of paragraphs from one to another.

Inline PERFORM

Execute statements inline without calling a separate paragraph.

TEST BEFORE vs TEST AFTER

TEST BEFORE (default) - Condition checked before execution
TEST AFTER - Condition checked after execution (executes at least once)

Best Practices

Use meaningful paragraph names
Keep paragraphs focused on single tasks
Avoid deeply nested PERFORMs
Always initialize loop counters

Code Example

       PROCEDURE DIVISION.
       MAIN-LOGIC.
           PERFORM INITIALIZE-ROUTINE.
           PERFORM PROCESS-DATA.
           PERFORM CLEANUP-ROUTINE.
           STOP RUN.

       * Simple PERFORM
       INITIALIZE-ROUTINE.
           MOVE ZEROS TO WS-COUNTER.
           MOVE SPACES TO WS-OUTPUT.

       * PERFORM TIMES
       PROCESS-DATA.
           PERFORM PRINT-LINE 10 TIMES.

       PRINT-LINE.
           DISPLAY "LINE NUMBER: " WS-COUNTER.
           ADD 1 TO WS-COUNTER.

       * PERFORM UNTIL
       READ-FILE-LOOP.
           PERFORM READ-RECORD UNTIL WS-EOF = "Y".

       READ-RECORD.
           READ INPUT-FILE
               AT END MOVE "Y" TO WS-EOF
               NOT AT END PERFORM PROCESS-RECORD
           END-READ.

       * PERFORM VARYING
       TABLE-SEARCH.
           PERFORM VARYING WS-IDX FROM 1 BY 1
               UNTIL WS-IDX > 100 OR WS-FOUND = "Y"
               IF WS-TABLE(WS-IDX) = WS-SEARCH-KEY
                   MOVE "Y" TO WS-FOUND
               END-IF
           END-PERFORM.

       * Inline PERFORM
       CALCULATE-TOTALS.
           PERFORM VARYING WS-I FROM 1 BY 1
               UNTIL WS-I > WS-COUNT
               ADD WS-AMOUNT(WS-I) TO WS-TOTAL
           END-PERFORM.

       * PERFORM WITH TEST AFTER
       GET-VALID-INPUT.
           PERFORM WITH TEST AFTER
               UNTIL WS-INPUT IS NUMERIC
               DISPLAY "ENTER A NUMBER: "
               ACCEPT WS-INPUT
           END-PERFORM.

       CLEANUP-ROUTINE.
           DISPLAY "PROCESSING COMPLETE".