IF THEN ELSE statement














IF THEN ELSE END-IF statement


     Format 

        IF condition-1  THEN   
                        Statements-1   
                        ..
        [ELSE statements-2 .. ]  

        [END-IF].


     - condition-1 is any of the conditions discussed in previoius pages
     - Statements-1 OR Statements-2 contains one or more COBOL statements
     - END-IF is the scope terminator. IF statement ends with this scope terminator
       Note : Instead of END-IF, we can use period as scope terminator.
              Structured programming rules recommends to use END-IF rather than period (.)
     - using THEN keyword is optional


     condition associated with IF statement , becomes true then all statements represented 
     by Statements-1 are get executed. Condition associated with IF statement , becomes 
     false then all statements represented by Statements-2 are get executed.  


     Below picture represents  what we discussed.

     



     Example.    IF  WS-A > ZERO  AND  WS-B > ZERO  THEN
                   COMPUTE POSITIVE-AMT = WS-A + WS-B
                 END-IF


     In the above example, COMPUTE statement execute only when the condition associated with
     IF statement becomes true. i.e., WS-A & WS-B should contains positive values.



     Example 2.   IF WS-A > ZER0  AND WS-B > ZERO  THEN
                     COMPUTE POSITIVE-AMT = WS-A + WS-B
                  ELSE
                     DISPLAY ' One of the input amount are not positive '
                     DISPLAY 'WS-A value ',  WS-A
                     DISPLAY 'WS-B value ', WS-B
                  END-IF.


     In this example, we have use ELSE keyword. If the condition associated with IF statement 
     is true then the COMPUTE statement will get executed.  If the condition is false, the 
     statements after ELSE keyword will get executed.
     
     
     Below picture represents what we discussed above.

     



                
     NEXT SENTENCE

         NEXT SENTENCE can be used in the place of either Statements-1 (THEN part) or Statements-2 
         (ELSE part) in IF statement. 

         - if there is no action required either in THEN part OR ELSE part of IF statement we can
           use this NEXT SENTENCE
         - It will transfer control to next statement after the nearest period 
         - Please make note that control wont pass to the next statement of END-IF, in this case.
           NEXT SENTENCE only check for closest period and execute the statements after that.


        Example -            
           
           MOVE 100 TO WS-A.
           MOVE 200 TO WS-B.
           MOVE 300 TO WS-C.
           
           IF WS-A > ZER0  AND WS-B > ZERO  THEN
               NEXT SENTENCE
           ELSE
               DISPLAY ' One of the input amount are not positive '
               DISPLAY 'WS-A value ',  WS-A
               DISPLAY 'WS-B value ', WS-B
           END-IF

           ADD  WS-A  TO WS-C.

           DISPLAY 'WS-C value', WS-C.


           Simple Test - Tell me what value will be displayed for the WS-C (last display statement 
                         in the above example) ? 

           Ans : 300 


        OK, let me explain, why the above example displayed 300 instead of 400.
        If you observe there is no period after END-IF, period is there after ADD statement. 
        Since the condition associated with IF statement is true, NEXT SENTENCE tranfered the 
        control to the statement after closest following period, then DISPLAY statement 
        displayed the WS-C value ADD statement did not get executed.


        Below picture shows the same what we discussed till now.

        



        If you  have a period after END-IF, WS-C value will be 400. because ADD statement will 
        get executed in this case. Quite interesting, isn't it?

        Normally we may face the interview question on differences between CONTINUE (cobol 85) 
        and NEXT SENTENCE (cobol 74). CONTINUE is dummy statement, control will continue as if 
        there are no statements, i.e., it wont do any control transfers.  In above example, if 
        you have CONTINUE statement instead of NEXT SENTENCE , o/p will be 400.




    Nested IF statements


        One IF statement can contain one or more IF statements within it.   
        As shown below.
        

        IF condition-1
            IF condition-2
                Statements-1
            ELSE 
                Statements-2
            END-IF
        ELSE
            IF condition-3
               Statements-3
            ELSE
               Statements-4
            END-IF
        END-IF

        -  In nested IF conditions, each END-IF paired with the preceding IF.
        -  It is suggested to use END-IF as scope terminator instead of period 
        -  In COBOL 74 we dont have END-IF scope terminator, need to use ELSE NEXT SENTENCE as
           and when required for proper pairing of ELSE part with IF statement. ( In COBOL 85
           we have END-IF, so it is suggested not to use period as scope terminator in nested 
           IF conditions for better readability and to reduce errors )