MODULE 4 · CONDITIONS · 5/8

EVALUATE

14 min30 XPExercise

A chain of IF ... ELSE IF ... ELSE IF gets hard to read fast. EVALUATE is COBOL's multi-way branch — like switch or case in other languages, but more powerful.

       IDENTIFICATION DIVISION.
       PROGRAM-ID. EVAL.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-GRADE    PIC X    VALUE "B".
       01  WS-SCORE    PIC 999  VALUE 72.
       PROCEDURE DIVISION.
           EVALUATE WS-GRADE
               WHEN "A"
                   DISPLAY "EXCELLENT"
               WHEN "B"
               WHEN "C"
                   DISPLAY "GRADE B OR C: PASS"
               WHEN "D" THRU "F"
                   DISPLAY "FAIL"
               WHEN OTHER
                   DISPLAY "UNKNOWN GRADE"
           END-EVALUATE
           EVALUATE WS-SCORE
               WHEN 0 THRU 49
                   DISPLAY "SCORE BAND: LOW"
               WHEN 50 THRU 79
                   DISPLAY "SCORE BAND: MIDDLE"
               WHEN OTHER
                   DISPLAY "SCORE BAND: HIGH"
           END-EVALUATE
           EVALUATE TRUE
               WHEN WS-SCORE > 90
                   DISPLAY "TOP"
               WHEN WS-SCORE > 70
                   DISPLAY "FIRST MATCH WINS: OVER 70"
               WHEN WS-SCORE > 60
                   DISPLAY "NEVER REACHED FOR 72"
           END-EVALUATE
           STOP RUN.

Output:

GRADE B OR C: PASS
SCORE BAND: MIDDLE
FIRST MATCH WINS: OVER 70

Evaluating a subject

EVALUATE WS-GRADE names a subject. Each WHEN gives a value to compare it with. COBOL checks the WHENs from the top, runs the statements of the first one that matches, and then jumps to END-EVALUATE. There is no fall-through into the next branch and no break to forget.

Several values, one action: stack WHENs with nothing between them (WHEN "B" / WHEN "C").
Ranges: WHEN 50 THRU 79 (or THROUGH) is inclusive at both ends. It works for alphanumeric values too: WHEN "D" THRU "F".
Default: WHEN OTHER catches everything not matched above. It must be last. If nothing matches and there's no WHEN OTHER, EVALUATE does nothing at all — which is how unhandled codes slip silently through a batch run.

EVALUATE TRUE

With EVALUATE TRUE, each WHEN holds a whole condition, and the first one that's true wins. That's the cleanest way to write a banded rule where later tests rely on earlier ones having failed: the third branch above is never reached for 72, because > 70 matched first. Order your WHENs from most specific to least.

Level-88 names fit naturally here:

           EVALUATE TRUE
               WHEN ACCT-ACTIVE
                   PERFORM PROCESS-ACTIVE
               WHEN ACCT-DORMANT
                   PERFORM PROCESS-DORMANT
               WHEN OTHER
                   PERFORM REPORT-BAD-STATUS
           END-EVALUATE

(PERFORM runs a paragraph; you'll meet it in the next module.)

Always write WHEN OTHER

Even when you believe every value is covered, add a WHEN OTHER that reports the unexpected value. Upstream systems add new codes without telling you. A program that ignores them silently is much harder to debug than one that says UNKNOWN TRANSACTION TYPE: Z.

On the job

EVALUATE is the standard way to dispatch on a transaction or record type in batch programs: one WHEN per type, each performing its own paragraph. Many shop standards forbid nested IFs deeper than two or three levels and ask for EVALUATE instead.

Your task

A bank's fee engine reads a one-character transaction type and an amount, one per line, and works out the fee:

Type	Meaning	Fee
`D`	deposit	0.00
`W` or `A`	branch or ATM withdrawal	1.50
`T`	transfer	depends on the amount, below

Transfer fees: amounts 0 to 999.99 → 2.00; 1,000.00 to 9,999.99 → 5.00; 10,000.00 and above → 15.00.

Display the type name and the fee through WS-FEE-OUT:

TYPE: TRANSFER
FEE:  5.00

The names are DEPOSIT, WITHDRAWAL (for both W and A) and TRANSFER. Any other type displays only:

UNKNOWN TRANSACTION TYPE: Z

Use EVALUATE for the type (with WHEN OTHER) and a second EVALUATE with THRU ranges for the transfer amount bands.

← Compound and abbreviated conditions EVALUATE ... ALSO decision tables →

Run your program to see its output here. The first visible test's input and datasets are used.

Submit to grade your program against every test.