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COBOL Condition Testing

Condition testing in COBOL involves evaluating various types of conditions to make decisions. Learn about IF statements, EVALUATE statements, and different condition types for effective decision-making.

Basic IF Statements

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       IF CUSTOMER-BALANCE > 1000
           DISPLAY 'High balance customer'
           PERFORM PROCESS-HIGH-BALANCE
       ELSE
           DISPLAY 'Standard customer'
           PERFORM PROCESS-STANDARD-CUSTOMER
       END-IF.

Use IF statements for simple true/false decisions. The condition is evaluated, and if true, the statements after IF execute. If false, the ELSE clause (if present) executes. Always use END-IF to close the statement.

Nested IF Statements

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       IF CUSTOMER-TYPE = 'I'
           IF CUSTOMER-BALANCE > 5000
               DISPLAY 'Premium individual customer'
               PERFORM PROCESS-PREMIUM-INDIVIDUAL
           ELSE
               DISPLAY 'Standard individual customer'
               PERFORM PROCESS-STANDARD-INDIVIDUAL
           END-IF
       ELSE IF CUSTOMER-TYPE = 'C'
           DISPLAY 'Corporate customer'
           PERFORM PROCESS-CORPORATE
       ELSE
           DISPLAY 'Unknown customer type'
           PERFORM PROCESS-UNKNOWN
       END-IF.

Nest IF statements for complex decision trees. Use ELSE IF for multiple conditions. Proper indentation makes nested logic easier to read and maintain. Each IF must have a corresponding END-IF.

EVALUATE Statements

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       EVALUATE CUSTOMER-STATUS
           WHEN 'A'
               DISPLAY 'Active customer'
               PERFORM PROCESS-ACTIVE
           WHEN 'I'
               DISPLAY 'Inactive customer'
               PERFORM PROCESS-INACTIVE
           WHEN 'S'
               DISPLAY 'Suspended customer'
               PERFORM PROCESS-SUSPENDED
           WHEN OTHER
               DISPLAY 'Unknown status'
               PERFORM PROCESS-UNKNOWN
       END-EVALUATE.

Use EVALUATE for multi-way decisions based on a single variable. It's cleaner than nested IF statements when you have many possible values. WHEN OTHER handles any values not explicitly listed.

Class Conditions

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       IF CUSTOMER-ID IS NUMERIC
           DISPLAY 'Valid numeric ID'
           PERFORM PROCESS-NUMERIC-ID
       ELSE
           DISPLAY 'Invalid non-numeric ID'
           PERFORM PROCESS-INVALID-ID
       END-IF.
       
       IF CUSTOMER-NAME IS ALPHABETIC
           DISPLAY 'Valid alphabetic name'
       ELSE
           DISPLAY 'Name contains non-letters'
       END-IF.

Class conditions test the type of data. NUMERIC tests if data contains only digits (0-9). ALPHABETIC tests if data contains only letters (A-Z, a-z). Use these for data validation and type checking.

Sign Conditions

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       IF TRANSACTION-AMOUNT IS POSITIVE
           DISPLAY 'Credit transaction'
           PERFORM PROCESS-CREDIT
       ELSE IF TRANSACTION-AMOUNT IS NEGATIVE
           DISPLAY 'Debit transaction'
           PERFORM PROCESS-DEBIT
       ELSE IF TRANSACTION-AMOUNT IS ZERO
           DISPLAY 'Zero amount transaction'
           PERFORM PROCESS-ZERO
       END-IF.

Sign conditions test the sign of numeric values. POSITIVE tests for values greater than zero, NEGATIVE for values less than zero, and ZERO for exactly zero. These are useful for financial calculations.

Complex Conditions

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       IF (CUSTOMER-TYPE = 'I' AND CUSTOMER-BALANCE > 1000)
           OR (CUSTOMER-TYPE = 'C' AND CUSTOMER-BALANCE > 5000)
           DISPLAY 'Eligible for premium service'
           PERFORM PROCESS-PREMIUM
       ELSE
           DISPLAY 'Standard service only'
           PERFORM PROCESS-STANDARD
       END-IF.

Combine conditions using AND, OR, and NOT operators. Use parentheses to control evaluation order. Complex conditions allow sophisticated business logic while keeping code readable.

EVALUATE with Multiple Conditions

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       EVALUATE TRUE
           WHEN CUSTOMER-TYPE = 'I' AND CUSTOMER-BALANCE > 1000
               PERFORM PROCESS-PREMIUM-INDIVIDUAL
           WHEN CUSTOMER-TYPE = 'I' AND CUSTOMER-BALANCE <= 1000
               PERFORM PROCESS-STANDARD-INDIVIDUAL
           WHEN CUSTOMER-TYPE = 'C' AND CUSTOMER-BALANCE > 5000
               PERFORM PROCESS-PREMIUM-CORPORATE
           WHEN CUSTOMER-TYPE = 'C' AND CUSTOMER-BALANCE <= 5000
               PERFORM PROCESS-STANDARD-CORPORATE
           WHEN OTHER
               PERFORM PROCESS-UNKNOWN-TYPE
       END-EVALUATE.

Use EVALUATE TRUE with WHEN clauses for complex multi-condition logic. This is cleaner than deeply nested IF statements and makes all conditions visible at the same level.

Condition Names

88-level condition names

Conditional Logic

Decision-making patterns