Conditional Logic in COBOL

COBOL's IF statement evaluates a condition and executes the statements following it when true, optionally followed by an ELSE clause for the false path. Modern COBOL requires an explicit END-IF scope terminator when the IF is nested inside another conditional or when the statement block contains a period-sensitive ambiguity, replacing the older style of relying on a period to end the whole statement. Conditions can be simple relation tests like WS-AGE >= 18, class tests like WS-FIELD IS NUMERIC, or sign tests like WS-BALANCE IS NEGATIVE, and any of these can be combined with AND, OR, and NOT to form compound conditions.

Nested IF statements let a program branch on multiple related conditions, but deep nesting quickly becomes hard to read and is a common source of bugs when a misplaced END-IF changes which ELSE binds to which IF. Compound conditions built with AND, OR, and NOT follow standard logical precedence where NOT binds tightest, then AND, then OR, so complex conditions should use parentheses explicitly rather than relying on memorized precedence rules. A well-known COBOL shorthand also lets you write WS-STATUS = "A" OR "B" OR "C" as an abbreviated compound relation condition, which the compiler expands to three full comparisons against WS-STATUS.

EVALUATE is COBOL's multi-branch conditional, roughly equivalent to a switch/case construct in other languages but considerably more flexible because each WHEN clause can test a different condition, a range with THRU, or even multiple subjects at once using EVALUATE TRUE with independent condition-names. Unlike a chain of nested IFs, EVALUATE clearly separates each branch and evaluates WHEN clauses in order, stopping at the first match, with WHEN OTHER catching any case not explicitly handled. EVALUATE TRUE is an especially common idiom because it lets each WHEN contain a full independent condition rather than being restricted to comparing a single subject.

An 88-level condition-name attaches a readable boolean name to one or more specific values of its parent field, letting you write IF WS-VALID-STATUS instead of IF WS-STATUS = "A" OR WS-STATUS = "P", which makes business rules self-documenting and centralizes the valid values in one place in the DATA DIVISION. Setting a condition-name true with SET WS-VALID-STATUS TO TRUE moves the first listed value into the parent field, which is a convenient shorthand when there is exactly one value to set but ambiguous when a condition-name covers a range or list of values. Condition-names are one of COBOL's most effective readability tools because they let procedural logic read like plain business English while keeping the underlying literal values maintainable in a single declaration.