COBOL - Loop Statements


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There are some tasks that need to be done over and over again like reading each record of a file till its end. The loop statements used in COBOL are −

  • Perform Thru
  • Perform Until
  • Perform Times
  • Perform Varying

Perform Thru

Perform Thru is used to execute a series of paragraph by giving the first and last paragraph names in the sequence. After executing the last paragraph, the control is returned back.

In-line Perform

Statements inside the PERFORM will be executed till END-PERFORM is reached.

Syntax

Following is the syntax of In-line perform −

PERFORM 
   DISPLAY 'HELLO WORLD'
END-PERFORM.

Out-of-line Perform

Here, a statement is executed in one paragraph and then the control is transferred to other paragraph or section.

Syntax

Following is the syntax of Out-of-line perform −

PERFORM PARAGRAPH1 THRU PARAGRAPH2

Example

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

PROCEDURE DIVISION.
   A-PARA.
   PERFORM DISPLAY 'IN A-PARA'
   END-PERFORM.
   PERFORM C-PARA THRU E-PARA.
   
   B-PARA.
   DISPLAY 'IN B-PARA'.
   STOP RUN.
   
   C-PARA.
   DISPLAY 'IN C-PARA'.
   
   D-PARA.
   DISPLAY 'IN D-PARA'.
   
   E-PARA.
   DISPLAY 'IN E-PARA'.

JCL to execute the above COBOL program.

//SAMPLE JOB(TESTJCL,XXXXXX),CLASS=A,MSGCLASS=C
//STEP1 EXEC PGM=HELLO

When you compile and execute the above program, it produces the following result −

IN A-PARA
IN C-PARA
IN D-PARA
IN E-PARA
IN B-PARA

Perform Until

In ‘perform until’, a paragraph is executed until the given condition becomes true. ‘With test before’ is the default condition and it indicates that the condition is checked before the execution of statements in a paragraph.

Syntax

Following is the syntax of perform until −

PERFORM A-PARA UNTIL COUNT=5

PERFORM A-PARA WITH TEST BEFORE UNTIL COUNT=5

PERFORM A-PARA WITH TEST AFTER UNTIL COUNT=5

Example

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 WS-CNT PIC 9(1) VALUE 0. 

PROCEDURE DIVISION.
   A-PARA.
   PERFORM B-PARA WITH TEST AFTER UNTIL WS-CNT>3.
   STOP RUN.
   
   B-PARA.
   DISPLAY 'WS-CNT : 'WS-CNT.
   ADD 1 TO WS-CNT.

JCL to execute the above COBOL program −

//SAMPLE JOB(TESTJCL,XXXXXX),CLASS=A,MSGCLASS=C
//STEP1 EXEC PGM=HELLO

When you compile and execute the above program, it produces the following result −

WS-CNT : 0
WS-CNT : 1
WS-CNT : 2
WS-CNT : 3

Perform Times

In ‘perform times’, a paragraph will be executed the number of times specified.

Syntax

Following is the syntax of perform times −

PERFORM A-PARA 5 TIMES.

Example

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

PROCEDURE DIVISION.
   A-PARA.
   PERFORM B-PARA 3 TIMES.
   STOP RUN.
   
   B-PARA.
   DISPLAY 'IN B-PARA'.

JCL to execute the above COBOL program −

//SAMPLE JOB(TESTJCL,XXXXXX),CLASS=A,MSGCLASS=C
//STEP1 EXEC PGM=HELLO

When you compile and execute the above program, it produces the following result −

IN B-PARA
IN B-PARA
IN B-PARA

Perform Varying

In perform varying, a paragraph will be executed till the condition in Until phrase becomes true.

Syntax

Following is the syntax of perform varying −

PERFORM A-PARA VARYING A FROM 1 BY 1 UNTIL A=5.

Example

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 WS-A PIC 9 VALUE 0.

PROCEDURE DIVISION.
   A-PARA.
   PERFORM B-PARA VARYING WS-A FROM 1 BY 1 UNTIL WS-A=5
   STOP RUN.
   
   B-PARA.
   DISPLAY 'IN B-PARA ' WS-A.

JCL to execute the above COBOL program −

//SAMPLE JOB(TESTJCL,XXXXXX),CLASS=A,MSGCLASS=C
//STEP1 EXEC PGM=HELLO

When you compile and execute the above program, it produces the following result −

IN B-PARA 1
IN B-PARA 2
IN B-PARA 3
IN B-PARA 4

GO TO Statement

GO TO statement is used to change the flow of execution in a program. In GO TO statements, transfer goes only in the forward direction. It is used to exit a paragraph. The different types of GO TO statements used are as follows −

Unconditional GO TO

GO TO para-name.

Conditional GO TO

GO TO para-1 para-2 para-3 DEPENDING ON x.

If 'x' is equal to 1, then the control will be transferred to the first paragraph; and if 'x' is equal to 2, then the control will be transferred to the second paragraph, and so on.

Example

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 WS-A PIC 9 VALUE 2.
   
PROCEDURE DIVISION.
   A-PARA.
   DISPLAY 'IN A-PARA'
   GO TO B-PARA.
   
   B-PARA.
   DISPLAY 'IN B-PARA '.
   GO TO C-PARA D-PARA DEPENDING ON WS-A.
   
   C-PARA.
   DISPLAY 'IN C-PARA '.
   
   D-PARA.
   DISPLAY 'IN D-PARA '.
   STOP RUN.

JCL to execute the above COBOL program:

//SAMPLE JOB(TESTJCL,XXXXXX),CLASS=A,MSGCLASS=C
//STEP1 EXEC PGM=HELLO

When you compile and execute the above program, it produces the following result:

IN A-PARA
IN B-PARA 
IN D-PARA 


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