COBOL Tutorial

COBOL Program Structure

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Introduction to COBOL Program Structure

Every COBOL program follows a standardized structure consisting of four main divisions. This structured approach ensures consistency, readability, and maintainability across all COBOL applications. Understanding this structure is fundamental to COBOL programming.

The Four Divisions

COBOL programs are organized into four distinct divisions, each serving a specific purpose:

IDENTIFICATION DIVISION - Program identification and documentation
ENVIRONMENT DIVISION - Hardware and software environment specifications
DATA DIVISION - Data definitions and file descriptions
PROCEDURE DIVISION - Program logic and executable statements

These divisions must appear in this exact order, and each division has specific rules about what can be included within it.

Basic Program Structure

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IDENTIFICATION DIVISION.
PROGRAM-ID. program-name.
 
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. computer-name.
OBJECT-COMPUTER. computer-name.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  variable-name PIC X(10).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    DISPLAY "Hello, World!"
    STOP RUN.

This is the minimal structure for a COBOL program. Each division can be expanded with additional entries depending on the program's requirements.

Division Hierarchy

Division	Required	Purpose	Content
IDENTIFICATION	Yes	Program identification	PROGRAM-ID, documentation
ENVIRONMENT	Yes	System configuration	Hardware, software, files
DATA	Yes	Data definitions	Variables, files, records
PROCEDURE	Yes	Program logic	Executable statements

IDENTIFICATION DIVISION

The IDENTIFICATION DIVISION serves as the program header and contains documentation about the program. It is the first division in every COBOL program and provides essential information for program identification and management.

Required and Optional Paragraphs

The IDENTIFICATION DIVISION contains one required paragraph and several optional ones:

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IDENTIFICATION DIVISION.
PROGRAM-ID. CUSTOMER-PROCESSING.
AUTHOR. JOHN DOE.
DATE-WRITTEN. 12/31/2023.
DATE-COMPILED. 01/15/2024.
SECURITY. CONFIDENTIAL.
REMARKS. This program processes customer data.

Only PROGRAM-ID is required. All other paragraphs are optional and serve documentation purposes.

PROGRAM-ID Paragraph

The PROGRAM-ID paragraph is mandatory and specifies the program name:

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* Basic PROGRAM-ID
PROGRAM-ID. SALES-REPORT.
 
* PROGRAM-ID with comment
PROGRAM-ID. CUSTOMER-MAINTENANCE.
 
* PROGRAM-ID with common name (optional)
PROGRAM-ID. INVENTORY-SYSTEM IS COMMON.

The program name must be unique within the system and follows COBOL naming conventions. The IS COMMON clause is optional and indicates the program can be called by other programs.

Documentation Paragraphs

Optional paragraphs provide additional documentation:

Paragraph	Purpose	Example
AUTHOR	Program author	AUTHOR. JOHN DOE.
DATE-WRITTEN	Creation date	DATE-WRITTEN. 12/31/2023.
DATE-COMPILED	Compilation date	DATE-COMPILED. 01/15/2024.
SECURITY	Security level	SECURITY. CONFIDENTIAL.
REMARKS	Additional notes	REMARKS. Customer data processing.

ENVIRONMENT DIVISION

The ENVIRONMENT DIVISION describes the computing environment in which the program will run. It specifies hardware and software dependencies, file configurations, and system-specific information. This division is required but can be minimal in modern COBOL implementations.

Division Structure

The ENVIRONMENT DIVISION consists of two main sections:

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ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IBM-3090.
OBJECT-COMPUTER. IBM-3090.
SPECIAL-NAMES.
    CURRENCY SIGN IS "$".
 
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT".
I-O-CONTROL.
    SAME RECORD AREA FOR CUSTOMER-FILE, BACKUP-FILE.

The CONFIGURATION SECTION describes the computing environment, while the INPUT-OUTPUT SECTION handles file configurations and I/O control.

CONFIGURATION SECTION

This section contains three main paragraphs:

Paragraph	Purpose	Example
SOURCE-COMPUTER	Development environment	SOURCE-COMPUTER. IBM-3090.
OBJECT-COMPUTER	Execution environment	OBJECT-COMPUTER. IBM-3090.
SPECIAL-NAMES	System-specific names	CURRENCY SIGN IS "$".

INPUT-OUTPUT SECTION

This section handles file and I/O configurations:

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INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS CUSTOMER-STATUS.
        
    SELECT REPORT-FILE
        ASSIGN TO "REPORT.TXT"
        ORGANIZATION IS LINE SEQUENTIAL.
 
I-O-CONTROL.
    SAME RECORD AREA FOR CUSTOMER-FILE, BACKUP-FILE
    APPLY WRITE-ONLY ON CUSTOMER-FILE.

FILE-CONTROL defines file characteristics, while I-O-CONTROL specifies I/O behavior and optimizations.

Modern Usage

In contemporary COBOL environments, the ENVIRONMENT DIVISION is often simplified:

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ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT".

Many modern COBOL compilers provide defaults for hardware specifications, making the CONFIGURATION SECTION optional in many cases.

DATA DIVISION

The DATA DIVISION defines all data structures used by the program. It describes variables, file records, constants, and data relationships. This division is required and contains the data definitions that the PROCEDURE DIVISION will manipulate.

Division Sections

The DATA DIVISION consists of three main sections:

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DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 80 CHARACTERS.
01  CUSTOMER-RECORD.
    05  CUSTOMER-ID       PIC X(5).
    05  CUSTOMER-NAME     PIC X(30).
    05  CUSTOMER-ADDRESS  PIC X(45).
 
WORKING-STORAGE SECTION.
01  WS-COUNTER           PIC 9(3) VALUE 0.
01  WS-TOTAL-AMOUNT      PIC 9(7)V99 VALUE 0.
01  WS-EOF-FLAG          PIC X VALUE 'N'.
    88  END-OF-FILE       VALUE 'Y'.
 
LINKAGE SECTION.
01  LS-PARAMETER         PIC X(10).

Each section serves a specific purpose in data management and program communication.

FILE SECTION

The FILE SECTION defines external file structures:

File Description (FD) - Defines file characteristics and record layouts
Record Descriptions - Define the structure of records within files
Report Section - Defines report layouts (when using Report Writer)

The FILE SECTION is required only when the program processes files. Each file used by the program must have a corresponding FD entry.

WORKING-STORAGE SECTION

The WORKING-STORAGE SECTION defines internal program variables:

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WORKING-STORAGE SECTION.
* Simple variables
01  WS-COUNTER           PIC 9(3) VALUE 0.
01  WS-TOTAL-AMOUNT      PIC 9(7)V99 VALUE 0.
01  WS-CUSTOMER-NAME     PIC X(30).
 
* Constants
01  WS-CONSTANTS.
    05  WS-MAX-RECORDS   PIC 9(5) VALUE 10000.
    05  WS-TAX-RATE      PIC V999 VALUE .08.
 
* Condition names
01  WS-EOF-FLAG          PIC X VALUE 'N'.
    88  END-OF-FILE       VALUE 'Y'.
    88  NOT-END-OF-FILE   VALUE 'N'.
 
* Group items
01  WS-DATE-FIELDS.
    05  WS-YEAR          PIC 9(4).
    05  WS-MONTH         PIC 9(2).
    05  WS-DAY           PIC 9(2).

WORKING-STORAGE variables exist only during program execution and are used for temporary data storage and calculations.

LINKAGE SECTION

The LINKAGE SECTION defines parameters passed between programs:

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LINKAGE SECTION.
* Input parameters
01  LS-CUSTOMER-ID       PIC X(5).
01  LS-ACTION-CODE       PIC X.
 
* Output parameters
01  LS-RETURN-CODE       PIC 9(2).
01  LS-ERROR-MESSAGE     PIC X(50).
 
* Complex parameter structure
01  LS-PARAMETER-BLOCK.
    05  LS-FUNCTION-CODE PIC X.
    05  LS-DATA-LENGTH   PIC 9(4).
    05  LS-DATA-AREA     PIC X(100).

The LINKAGE SECTION is used when programs communicate with each other or when the program receives parameters from the calling environment.

Section Requirements

Section	Required	When Used
FILE SECTION	No	When processing files
WORKING-STORAGE SECTION	No	When using variables
LINKAGE SECTION	No	When receiving parameters

PROCEDURE DIVISION

The PROCEDURE DIVISION contains all the executable statements and program logic. It is the heart of the COBOL program where the actual processing occurs. This division is required and contains the instructions that tell the computer what to do.

Division Structure

The PROCEDURE DIVISION consists of paragraphs and sections:

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PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-DATA
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    OPEN OUTPUT REPORT-FILE
    MOVE 0 TO WS-RECORD-COUNT.
 
PROCESS-DATA.
    PERFORM UNTIL END-OF-FILE
        READ CUSTOMER-FILE
            AT END
                MOVE 'Y' TO WS-EOF-FLAG
            NOT AT END
                ADD 1 TO WS-RECORD-COUNT
                PERFORM PROCESS-RECORD
        END-READ
    END-PERFORM.
 
PROCESS-RECORD.
    MOVE CUSTOMER-NAME TO REPORT-LINE
    WRITE REPORT-LINE.
 
FINALIZATION.
    CLOSE CUSTOMER-FILE
    CLOSE REPORT-FILE
    DISPLAY "Processed " WS-RECORD-COUNT " records".

The PROCEDURE DIVISION is organized into logical paragraphs that group related operations together.

Paragraphs and Sections

The PROCEDURE DIVISION uses two levels of organization:

Paragraphs - Named groups of statements (e.g., MAIN-PROCESS, INITIALIZATION)
Sections - Named groups of paragraphs (optional, used for complex programs)

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PROCEDURE DIVISION.
FILE-PROCESSING SECTION.
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    OPEN OUTPUT REPORT-FILE.
 
DATA-PROCESSING SECTION.
MAIN-PROCESS.
    PERFORM PROCESS-RECORDS UNTIL END-OF-FILE.
 
PROCESS-RECORDS.
    READ CUSTOMER-FILE
    PERFORM CALCULATE-TOTALS.
 
CALCULATE-TOTALS.
    ADD CUSTOMER-AMOUNT TO WS-TOTAL.
 
FINALIZATION SECTION.
CLEANUP.
    CLOSE CUSTOMER-FILE
    CLOSE REPORT-FILE.

Common Statement Types

The PROCEDURE DIVISION contains various types of executable statements:

Statement Type	Purpose	Example
File Operations	Open, read, write, close files	OPEN INPUT CUSTOMER-FILE
Data Movement	Move data between fields	MOVE CUSTOMER-NAME TO WS-NAME
Arithmetic	Perform calculations	ADD AMOUNT TO TOTAL
Control Flow	Conditional and loop logic	IF AMOUNT > 1000
Program Control	Call other programs	CALL "SUBPROGRAM"

Program Flow

A typical COBOL program follows this general flow:

Initialization - Set up program environment, open files, initialize variables
Main Processing - Perform the primary program logic
Cleanup - Close files, display results, perform final operations
Termination - End the program with STOP RUN

Complete Program Examples

These examples demonstrate complete COBOL programs with all four divisions properly structured and organized.

Example 1: Simple Hello World Program

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IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO-WORLD.
AUTHOR. JOHN DOE.
DATE-WRITTEN. 12/31/2023.
 
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IBM-3090.
OBJECT-COMPUTER. IBM-3090.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-MESSAGE          PIC X(20) VALUE "Hello, World!".
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    DISPLAY WS-MESSAGE
    STOP RUN.

This minimal program demonstrates the basic structure with all required divisions.

Example 2: File Processing Program

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IDENTIFICATION DIVISION.
PROGRAM-ID. CUSTOMER-PROCESSING.
AUTHOR. JANE SMITH.
DATE-WRITTEN. 12/31/2023.
REMARKS. This program processes customer records.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS CUSTOMER-STATUS.
        
    SELECT REPORT-FILE ASSIGN TO "REPORT.TXT"
        ORGANIZATION IS LINE SEQUENTIAL
        FILE STATUS IS REPORT-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 80 CHARACTERS.
01  CUSTOMER-RECORD.
    05  CUSTOMER-ID       PIC X(5).
    05  CUSTOMER-NAME     PIC X(30).
    05  CUSTOMER-ADDRESS  PIC X(45).
 
WORKING-STORAGE SECTION.
01  CUSTOMER-STATUS       PIC XX.
01  REPORT-STATUS         PIC XX.
01  WS-RECORD-COUNT       PIC 9(5) VALUE 0.
01  WS-EOF-FLAG           PIC X VALUE 'N'.
    88  END-OF-FILE         VALUE 'Y'.
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-RECORDS
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    OPEN OUTPUT REPORT-FILE
    IF CUSTOMER-STATUS NOT = "00"
        DISPLAY "Error opening customer file: " CUSTOMER-STATUS
        STOP RUN
    END-IF.
 
PROCESS-RECORDS.
    PERFORM UNTIL END-OF-FILE
        READ CUSTOMER-FILE
            AT END
                MOVE 'Y' TO WS-EOF-FLAG
            NOT AT END
                ADD 1 TO WS-RECORD-COUNT
                PERFORM WRITE-REPORT-LINE
        END-READ
    END-PERFORM.
 
WRITE-REPORT-LINE.
    MOVE CUSTOMER-NAME TO REPORT-LINE
    WRITE REPORT-LINE.
 
FINALIZATION.
    CLOSE CUSTOMER-FILE
    CLOSE REPORT-FILE
    DISPLAY "Processed " WS-RECORD-COUNT " customer records".

This program demonstrates file processing with proper error handling and structured program flow.

Example 3: Subprogram with Parameters

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IDENTIFICATION DIVISION.
PROGRAM-ID. CALCULATE-TAX.
AUTHOR. BOB JOHNSON.
DATE-WRITTEN. 12/31/2023.
REMARKS. Subprogram to calculate tax amount.
 
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IBM-3090.
OBJECT-COMPUTER. IBM-3090.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-TAX-RATE          PIC V999 VALUE .08.
 
LINKAGE SECTION.
01  LS-AMOUNT            PIC 9(7)V99.
01  LS-TAX-AMOUNT        PIC 9(7)V99.
01  LS-RETURN-CODE       PIC 9(2).
 
PROCEDURE DIVISION USING LS-AMOUNT, LS-TAX-AMOUNT, LS-RETURN-CODE.
MAIN-PROCESS.
    PERFORM CALCULATE-TAX
    PERFORM SET-RETURN-CODE
    EXIT PROGRAM.
 
CALCULATE-TAX.
    COMPUTE LS-TAX-AMOUNT = LS-AMOUNT * WS-TAX-RATE.
 
SET-RETURN-CODE.
    MOVE 0 TO LS-RETURN-CODE.

This subprogram demonstrates the use of the LINKAGE SECTION for parameter passing.

Best Practices and Guidelines

Following these best practices ensures well-structured, maintainable COBOL programs.

Division Organization

Always include all four divisions in the correct order
Use meaningful program names that clearly identify the program's purpose
Include documentation paragraphs in the IDENTIFICATION DIVISION
Organize DATA DIVISION sections logically (FILE, WORKING-STORAGE, LINKAGE)
Structure PROCEDURE DIVISION with clear, descriptive paragraph names

Naming Conventions

Use descriptive names for programs, variables, and paragraphs
Follow consistent prefixes (WS- for working storage, LS- for linkage)
Use hyphens to separate words in COBOL names
Avoid reserved words when naming data items
Keep names reasonably short but descriptive

Program Structure

Organize paragraphs logically (initialization, main processing, cleanup)
Use PERFORM statements to call paragraphs and maintain structure
Include error handling for file operations and data validation
Add comments to explain complex logic or business rules
Keep paragraphs focused on a single responsibility

Common Pitfalls to Avoid

Missing PROGRAM-ID in the IDENTIFICATION DIVISION
Incorrect division order - divisions must appear in the specified sequence
Undefined data items - all variables must be defined before use
Missing STOP RUN - programs should have a clear termination point
Poor paragraph organization - unclear program flow and structure
Inconsistent naming - makes programs difficult to maintain

Test Your Knowledge

1. What are the four main divisions of a COBOL program?

IDENTIFICATION, ENVIRONMENT, DATA, PROCEDURE
HEADER, BODY, FOOTER, MAIN
DECLARATION, INITIALIZATION, PROCESSING, TERMINATION
PROGRAM, FILE, WORKING, LOGIC

2. Which division contains the actual program logic and executable statements?

IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION

3. What is the purpose of the ENVIRONMENT DIVISION?

To define program variables
To specify hardware and software dependencies
To contain program logic
To identify the program

4. Which section of the DATA DIVISION is required in all COBOL programs?

FILE SECTION
WORKING-STORAGE SECTION
LINKAGE SECTION
None of the above

5. What is the minimum required entry in the IDENTIFICATION DIVISION?

PROGRAM-ID
AUTHOR
DATE-WRITTEN
All of the above

COBOL Tutorial

COBOL Program Structure

Introduction to COBOL Program Structure

The Four Divisions

Basic Program Structure

Division Hierarchy

IDENTIFICATION DIVISION

Required and Optional Paragraphs

PROGRAM-ID Paragraph

Documentation Paragraphs

ENVIRONMENT DIVISION

Division Structure

CONFIGURATION SECTION

INPUT-OUTPUT SECTION

Modern Usage

DATA DIVISION

Division Sections

FILE SECTION

WORKING-STORAGE SECTION

LINKAGE SECTION

Section Requirements

PROCEDURE DIVISION

Division Structure

Paragraphs and Sections

Common Statement Types

Program Flow

Complete Program Examples

Example 1: Simple Hello World Program

Example 2: File Processing Program

Example 3: Subprogram with Parameters

Best Practices and Guidelines

Division Organization

Naming Conventions

Program Structure

Common Pitfalls to Avoid

Test Your Knowledge

Frequently Asked Questions

What is the purpose of the IDENTIFICATION DIVISION?

Can a COBOL program have multiple ENVIRONMENT DIVISION entries?

What is the difference between the FILE SECTION and WORKING-STORAGE SECTION?

Is the PROCEDURE DIVISION required in all COBOL programs?

What is the purpose of the LINKAGE SECTION in the DATA DIVISION?

Related Concepts

IDENTIFICATION DIVISION

ENVIRONMENT DIVISION

DATA DIVISION Sections

PROCEDURE DIVISION

File Description (FD)

Related Pages