Quyết định với IF và ĐÁNH GIÁ

Decision making in COBOL is performed primarily using the IF conditional statement and the multi-branch selection structure EVALUATE (analogous to switch or match in modern languages).

The IF Conditional Statement

The fundamental syntax of the IF statement is:

IF condition
    statements-if-true
ELSE
    statements-if-false
END-IF.

In modern COBOL versions (COBOL-85 and later), the statement must explicitly end with END-IF. instead of relying solely on the final period ., significantly reducing parsing and logic errors.

Common Conditions

• Greater than: > or GREATER THAN
• Less than: < or LESS THAN
• Equal to: = or EQUAL TO
• Greater than or equal to: >= or GREATER THAN OR EQUAL TO
• Less than or equal to: <= or LESS THAN OR EQUAL TO

IF WS-BALANCE < 0
    DISPLAY "OVERDRAWN"
ELSE
    DISPLAY "ACCOUNT ACTIVE"
END-IF.

The EVALUATE Statement

When we need to compare a variable against multiple discrete values, nested IF statements can become complex. The EVALUATE statement resolves this by structuring the choices in a clean way:

EVALUATE WS-USER-ROLE
    WHEN "ADMIN"
        DISPLAY "FULL ACCESS"
    WHEN "EDITOR"
        DISPLAY "EDIT ACCESS"
    WHEN OTHER
        DISPLAY "LIMITED ACCESS"
END-EVALUATE.

• WHEN OTHER: Identifies the fallback branch (equivalent to default or the final else in modern languages).
• END-EVALUATE.: Closes the structure.

Try it yourself