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COBOL has a built-in report-generation feature: REPORT WRITER. It declaratively describes a report's structure and the runtime emits formatted output.

Most shops moved to manual formatting (PERFORM + edit pictures) for flexibility, but Report Writer remains in many production systems.

Anatomy

       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT REPORT-FILE ASSIGN TO 'output.txt'.

       DATA DIVISION.
       FILE SECTION.
       FD REPORT-FILE.
       01 REPORT-LINE PIC X(80).

       REPORT SECTION.
       RD SALES-REPORT
           CONTROLS ARE FINAL REGION DEPT
           PAGE LIMIT 60 LINES
               HEADING 1
               FIRST DETAIL 5
               LAST DETAIL 55.

       01 TYPE PAGE HEADING.
           02 LINE 1 COLUMN 25 PIC X(15) VALUE 'SALES BY DEPT'.
           02 LINE 3 COLUMN 1  PIC X(10) VALUE 'REGION'.
           02 LINE 3 COLUMN 12 PIC X(10) VALUE 'DEPT'.
           02 LINE 3 COLUMN 23 PIC X(10) VALUE 'SALES'.

       01 DETAIL-LINE TYPE DETAIL.
           02 COLUMN 1  PIC X(10) SOURCE REGION-IN.
           02 COLUMN 12 PIC X(10) SOURCE DEPT-IN.
           02 COLUMN 23 PIC $$$,$$9.99 SOURCE AMOUNT-IN.

       01 TYPE CONTROL FOOTING DEPT.
           02 COLUMN 1  PIC X(15) VALUE 'DEPT TOTAL:'.
           02 COLUMN 23 PIC $$$$,$$9.99 SUM AMOUNT-IN.

       01 TYPE CONTROL FOOTING FINAL.
           02 COLUMN 1  PIC X(15) VALUE 'GRAND TOTAL:'.
           02 COLUMN 23 PIC $$$$$,$$9.99 SUM AMOUNT-IN.

       PROCEDURE DIVISION.
           OPEN OUTPUT REPORT-FILE.
           INITIATE SALES-REPORT.
           PERFORM UNTIL END-OF-INPUT
               READ INPUT-FILE AT END SET END-OF-INPUT TO TRUE
               GENERATE DETAIL-LINE
           END-PERFORM.
           TERMINATE SALES-REPORT.
           CLOSE REPORT-FILE.
           STOP RUN.

What's happening

• RD (Report Description) — defines the report layout
• PAGE LIMIT — page size
• TYPE PAGE HEADING — runs at top of each page
• TYPE DETAIL — runs per record
• TYPE CONTROL FOOTING — runs when a control field changes (auto-subtotals)
• INITIATE — start the report
• GENERATE — emit one detail line
• TERMINATE — finish, emit final footings

The runtime tracks:

• Page breaks
• Control breaks (when REGION or DEPT changes)
• Subtotals (the SUM clauses accumulate automatically)
• Headings on each page

Why it's clever

For 1980s mainframe reports, this declarative model was elegant — describe the shape, let the runtime handle pagination and subtotals. No manual page counters, no manual subtotal accumulators, no manual heading reprinting.

Why most modern code skips it

• Limited flexibility — what if you want HTML output? Subtotals on multiple keys with custom logic?
• Hard to debug — the runtime hides the work
• Modern preference: explicit code, predictable behavior

That said, maintaining COBOL means understanding REPORT WRITER. Many production reports were written in it — and rewriting them as procedural code is a significant migration.

Modern alternatives

• Procedural code with edit pictures (covered in Fundamentals)
• External report tools (Crystal Reports, etc.) consuming COBOL output
• Database-backed reporting (move data to SQL, run reports there)
• Modern programming languages alongside COBOL via JNI/CALL bridges

For Judge0 we can't easily run a report file, but the pattern is critical to know if you're touching mainframe code.