COBOL ALTER Statement

COBOL ALTER Statement

ALTER dynamically changes the target of a GO TO statement at runtime. This statement is obsolete and should be avoided.

Syntax

```cobol ALTER procedure-name-1 TO PROCEED TO procedure-name-2 ```

How It Works

Changes where a GO TO statement will transfer control.

Example

```cobol GO-PARA. GO TO DEFAULT-PARA.

... ALTER GO-PARA TO PROCEED TO SPECIAL-PARA. ```

Why Avoid ALTER

• Creates unpredictable program flow
• Makes debugging extremely difficult
• Code becomes hard to maintain
• Not thread-safe
• Considered harmful practice

Alternatives

• Use EVALUATE for multi-way branching
• Use 88-level conditions
• Use PERFORM THRU with conditions

       IDENTIFICATION DIVISION.
       PROGRAM-ID. ALTER-DEMO.
      * NOTE: ALTER is obsolete - shown for legacy code
       PROCEDURE DIVISION.
       MAIN-PARA.
           GO TO INITIAL-PARA.
       PROCESS-PARA.
           DISPLAY 'In PROCESS-PARA'
           GO TO END-PARA.
       INITIAL-PARA.
           DISPLAY 'First call - setting up'
           ALTER PROCESS-PARA TO PROCEED TO MODIFIED-PARA
           GO TO PROCESS-PARA.
       MODIFIED-PARA.
           DISPLAY 'In MODIFIED-PARA'
           GO TO END-PARA.
       END-PARA.
           STOP RUN.