Why COBOL still, and what it is good at

COBOL was designed so that business people could read it. That makes it wordy, and it also makes forty-year-old code comprehensible to someone who has never seen it before — which turns out to be worth a great deal.

The design decisions that still matter

Fixed-point decimal arithmetic. COBOL computes money in decimal, exactly. A language using binary floating point cannot represent 0.10 exactly; COBOL's PIC S9(9)V99 COMP-3 can. For financial work this is not a preference, it is a requirement.
Data described separately from logic. Record layouts live in the DATA DIVISION and are shared between programs through copybooks. Change the layout in one place and every program picks it up on recompile.
Verbose, English-like syntax. ADD 1 TO WS-COUNTER is not clever, and that is the point. Someone unfamiliar with the codebase can follow it.
No pointers by default, no dynamic memory in classic style. Programs are predictable and their storage requirements are known before they run.

What it is not good at

COBOL has no rich standard library, limited string handling by modern standards, and a type system that will happily let you move a character field into a numeric one and only complain at run time — which is exactly how S0C7 abends happen. Modern COBOL has objects, JSON parsing and calls into other languages, but most production code does not use them.

A complete, small program

Count records and total an amount

       IDENTIFICATION DIVISION.
       PROGRAM-ID. PAYSUM.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT PAY-FILE ASSIGN TO INFILE
               ORGANIZATION IS SEQUENTIAL
               FILE STATUS IS WS-STATUS.
       DATA DIVISION.
       FILE SECTION.
       FD  PAY-FILE.
       01  PAY-RECORD.
           05  PAY-EMP-ID        PIC X(08).
           05  PAY-NAME          PIC X(30).
           05  PAY-AMOUNT        PIC S9(7)V99 COMP-3.
           05  FILLER            PIC X(20).
       WORKING-STORAGE SECTION.
       01  WS-STATUS             PIC XX     VALUE SPACES.
       01  WS-EOF-FLAG           PIC X      VALUE 'N'.
           88  END-OF-FILE                  VALUE 'Y'.
       01  WS-COUNT              PIC 9(07)  VALUE ZERO.
       01  WS-TOTAL              PIC S9(11)V99 COMP-3 VALUE ZERO.
       01  WS-TOTAL-ED           PIC ZZZ,ZZZ,ZZ9.99-.
       PROCEDURE DIVISION.
       0000-MAIN.
           PERFORM 1000-OPEN
           PERFORM 2000-PROCESS UNTIL END-OF-FILE
           PERFORM 3000-CLOSE
           GOBACK.
       1000-OPEN.
           OPEN INPUT PAY-FILE
           IF WS-STATUS NOT = '00'
               DISPLAY 'OPEN FAILED, STATUS ' WS-STATUS
               MOVE 12 TO RETURN-CODE
               GOBACK
           END-IF
           PERFORM 2100-READ.
       2000-PROCESS.
           ADD 1 TO WS-COUNT
           ADD PAY-AMOUNT TO WS-TOTAL
           PERFORM 2100-READ.
       2100-READ.
           READ PAY-FILE
               AT END SET END-OF-FILE TO TRUE
           END-READ.
       3000-CLOSE.
           CLOSE PAY-FILE
           MOVE WS-TOTAL TO WS-TOTAL-ED
           DISPLAY 'RECORDS READ : ' WS-COUNT
           DISPLAY 'TOTAL AMOUNT : ' WS-TOTAL-ED.

The design decisions that still matter

What it is not good at

A complete, small program

Common mistakes

What you will see at work

Key terms