This format is similar to “FOR loop” of other programming language
Syntax:-
PERFORM [para-1 [{THRU/THROUGH} para-n]]
VARYING id-1 FROM id-2
BY id-3 UNTIL condition-1
[statement-block END-PERFORM]
Where,
para-1, para-n are paragraph names which we want to call
id-1 can be numeric data item or index data item
id-2 can be numeric data item or index data item or literal
id-3 can be numeric data item or literal
condition-1 is any conditional-expression which can return either true or false
[statement-block END-PERFORM] is used for Inline PERFORM.
The PERFORM in this format work like this:-
First initializes id-1 with id-2. The condition is checked.
If the condition is false, execute the para-1 through para-n and then increment the id-1 by id-3 and again test the condition(s)
If the condition evaluates to false again, then again perform para-1 though para-n.
Repeat this process until the condition is met and evaluates to true. Once condition evaluates to true then loop is braked and the next statement following PERFORM will be executed
IN PARA-0
WS-INDEX: 10
IN PARA-1 WS-INDEX: 1
IN PARA-1 WS-INDEX: 2
IN PARA-0 AGAIN
In above example, if you observe, before PERFORM statement is executed, WS-INDEX was having value 10 but when PERFORM statement is executed for the first time it initialized WS-INDEX to 1 and since condition evaluates to false, it performed PARA-1. In second time it incremented WS-INDEX by 1 and then again called PARA-1 because condition ‘WS-INDEX =3’ evaluates to false. After that, again WS-INDEX incremented by 1 but this time condition is met and thus PARA-1 is not called and control is transferred to next statement following PERFORM
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