MODULE 3 · ARITHMETIC · 1/8

ADD and SUBTRACT

12 min30 XPExercise

COBOL was designed so a business analyst could read the arithmetic. Instead of balance = balance + deposit you write a sentence:

           ADD WS-DEPOSIT TO WS-BALANCE

That statement changes WS-BALANCE: the value of WS-DEPOSIT is added to it and the result replaces what was there. The field after TO is both an input and the receiving field.

The TO form

You can add several values at once, and even into several receivers:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. ADDTO.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-A      PIC 9(3) VALUE 10.
       01  WS-B      PIC 9(3) VALUE 20.
       01  WS-C      PIC 9(3) VALUE 5.
       PROCEDURE DIVISION.
           ADD WS-A TO WS-B
           DISPLAY WS-A " " WS-B
           ADD WS-A WS-C TO WS-B
           DISPLAY WS-B
           ADD 1 TO WS-B WS-C
           DISPLAY WS-B " " WS-C
           STOP RUN.

Output:

010 030
045
046 006

ADD WS-A WS-C TO WS-B adds both values to WS-B. ADD 1 TO WS-B WS-C adds 1 to each receiver. The sending fields (WS-A) never change.

The GIVING form

When you want to keep the inputs untouched, use GIVING. The result goes only into the field after GIVING, and whatever was there before is replaced:

           ADD WS-OPENING WS-DEPOSIT GIVING WS-TOTAL-IN

You will also meet ADD WS-A TO WS-B GIVING WS-C. With GIVING, the TO is just noise: WS-B is not changed, only WS-C receives the sum. Read GIVING as "the answer goes here and nowhere else".

SUBTRACT ... FROM

SUBTRACT mirrors ADD. Everything before FROM is summed, then taken away from the field after FROM:

           SUBTRACT WS-FEE WS-WITHDRAWAL FROM WS-BALANCE
           SUBTRACT WS-DISCOUNT FROM WS-PRICE GIVING WS-NET

The second form leaves WS-PRICE alone and puts the difference in WS-NET.

Unsigned fields lose the sign

If the receiving field has no S in its picture, a negative result is stored without its sign. With WS-A PIC 9(3) VALUE 10, SUBTRACT 50 FROM WS-A leaves 040, not -040. Any field that could go negative (balances, adjustments, variances) must be PIC S9....

Decimal alignment is automatic

Fields with different numbers of implied decimals (V) line up correctly: adding a PIC 9(3)V99 to a PIC 9(5)V9(4) works on the decimal point, just as you would on paper. You never shift values by hand.

On the job

In batch programs you will see long runs of ADD WS-TXN-AMT TO WS-DAILY-TOTAL style statements accumulating totals for reports. Reviewers like them because they are unambiguous: exactly one field changes, and it's named right there.

Your task

A teller program reads three amounts, one per line: the opening balance, a deposit and a withdrawal, typed with a decimal point. The input fields are declared PIC 9(7)V99 — wider than the values need, because GnuCOBOL's ACCEPT reads only as many characters as the field has digit positions.

Use ADD ... GIVING to put opening balance + deposit into WS-BALANCE.
Use SUBTRACT ... FROM to take the withdrawal off WS-BALANCE.
Display the balance through the edited field that is already declared.

For input 1000.00, 250.50, 100.25 the output is:

CLOSING BALANCE:  1,150.25

Don't use COMPUTE — that comes later in this module.

← Challenge: format a payslip MULTIPLY and DIVIDE →

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.