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COBOL

Breakdown of COBOL Syntax

COBOL (Common Business-Oriented Language) is one of the oldest programming languages, developed in the 1950s, primarily for business, finance, and administrative systems. It has a very verbose and readable syntax, designed to be close to natural language. It’s still used today in legacy systems, especially in banking, government, and insurance sectors.

1. Structure of a COBOL Program

A COBOL program is typically divided into four divisions:

  1. Identification Division: Provides metadata about the program.
  2. Environment Division: Defines the environment in which the program will run (e.g., file handling).
  3. Data Division: Describes the data structures and variables used by the program.
  4. Procedure Division: Contains the executable logic of the program.

Example of a basic COBOL program:

IDENTIFICATION DIVISION.
PROGRAM-ID. HelloWorld.

ENVIRONMENT DIVISION.

DATA DIVISION.

PROCEDURE DIVISION.
    DISPLAY "Hello, World!".
    STOP RUN.

2. Identification Division

The Identification Division contains the program’s name and other metadata. It’s mostly used for documentation and metadata purposes.

IDENTIFICATION DIVISION.
PROGRAM-ID. HelloWorld.
AUTHOR. John Doe.
DATE-WRITTEN. 2025-03-01.
  • PROGRAM-ID: Specifies the name of the program (required).
  • AUTHOR: Provides the name of the author.
  • DATE-WRITTEN: Specifies when the program was written.

3. Environment Division

The Environment Division defines the environment the program will operate in, such as file handling.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT inputFile ASSIGN TO 'INPUT.TXT'.
  • INPUT-OUTPUT SECTION: Used for defining input and output files or devices.
  • FILE-CONTROL: Defines how files are handled in the program.

4. Data Division

The Data Division describes all the variables, file formats, and data structures used in the program. It is divided into sections like File Section, Working-Storage Section, and Local-Storage Section.

Example of declaring variables:

DATA DIVISION.
WORKING-STORAGE SECTION.
01 user-name        PIC X(20).
01 user-age         PIC 99.
01 user-salary      PIC 9(5)V99.
  • WORKING-STORAGE SECTION: This section is used to define variables that will be used during program execution.
  • PIC: Specifies the data type and size.
    • PIC X(n): String of length n.
    • PIC 9(n): Numeric value with n digits.
    • PIC 9(n)V99: Numeric value with an implied decimal point.

5. Procedure Division

The Procedure Division is where the logic of the program resides. This is where computations, decisions, and data manipulations take place. It uses a declarative and verbose syntax.

Example of displaying a message:

PROCEDURE DIVISION.
    DISPLAY "Enter your name: ".
    ACCEPT user-name.
    DISPLAY "Hello, " user-name.
    STOP RUN.
  • DISPLAY: Outputs a message or value to the screen.
  • ACCEPT: Reads input from the user or from a file.

Example of a simple calculation:

PROCEDURE DIVISION.
    ADD 10 TO user-age.
    DISPLAY "User's new age: " user-age.
    STOP RUN.
  • ADD: Adds a value to a variable.
  • DISPLAY: Outputs the result to the screen.

6. Control Structures

COBOL has standard control flow mechanisms like IF-ELSE, PERFORM (loops), and EVALUATE (similar to switch-case).

IF-ELSE Statement

IF user-age > 18
    DISPLAY "Adult".
ELSE
    DISPLAY "Minor".
END-IF.
  • IF: Begins a conditional block.
  • ELSE: Executes an alternative block if the condition is false.

PERFORM Loop (For Iteration)

PERFORM 10 TIMES
    DISPLAY "Iteration: " counter
    ADD 1 TO counter.
END-PERFORM.
  • PERFORM: Repeats a section of code a specified number of times.
  • ADD: Used to increment a counter or modify a variable.

EVALUATE (Switch-Case Equivalent)

EVALUATE user-age
    WHEN 18
        DISPLAY "Just an adult."
    WHEN 19
        DISPLAY "Young adult."
    WHEN OTHER
        DISPLAY "Other age."
END-EVALUATE.
  • EVALUATE: Acts as a switch-case or if-else statement, matching values to blocks of code.

7. File Handling

COBOL has extensive support for file handling, typically in the File Section of the Data Division. It supports sequential, indexed, and relative files.

Example of reading a file:

FILE-CONTROL.
    SELECT inputFile ASSIGN TO 'INPUT.TXT'
        ORGANIZATION IS LINE SEQUENTIAL.

DATA DIVISION.
FILE SECTION.
FD  inputFile.
01  inputFileRecord PIC X(100).

PROCEDURE DIVISION.
OPEN INPUT inputFile.
READ inputFile INTO inputFileRecord.
DISPLAY inputFileRecord.
CLOSE inputFile.
  • FD (File Description): Specifies the file’s format.
  • OPEN INPUT: Opens a file for reading.
  • READ: Reads data from the file into a variable.
  • CLOSE: Closes the file when done.

8. Arrays (Tables)

COBOL allows arrays, called tables, to hold multiple items of the same type.

DATA DIVISION.
WORKING-STORAGE SECTION.
01  employee-table.
    05  employee-name OCCURS 10 TIMES PIC X(20).

PROCEDURE DIVISION.
    MOVE "John Doe" TO employee-name (1).
    DISPLAY employee-name (1).
  • OCCURS: Defines the number of elements in the array.
  • INDEXING: Arrays are accessed using indices, such as (1) for the first element.

9. Subroutines (Called Programs)

COBOL allows calling other programs or subroutines within the same or other COBOL programs.

PROCEDURE DIVISION.
    CALL "subprogram" USING employee-name.
    STOP RUN.
  • CALL: Invokes another COBOL program or subroutine.

10. Error Handling (Declarative Section)

COBOL supports error handling using DECLARATIVES and USE.

DECLARATIVES.
   FILE-ERROR HANDLER.
   PROCEDURE DIVISION.
       IF file-status = "00"
           DISPLAY "File is open."
       ELSE
           DISPLAY "Error: " file-status.
       END-IF.
  • FILE-ERROR HANDLER: A declarative part that handles file errors.

Summary of Key Points:

  • COBOL is designed for business data processing, with a focus on readability and verbosity.
  • Program Structure: Divided into Identification, Environment, Data, and Procedure divisions.
  • Variables: Declared in the Data Division, using PIC to define data types.
  • Control Flow: Includes IF-ELSE, PERFORM loops, and EVALUATE for conditional logic.
  • File Handling: Supports different file types like sequential and indexed files.
  • Procedures and Subroutines: Programs are modular, and subroutines can be called using CALL.
  • Arrays (Tables): COBOL uses OCCURS to define arrays with fixed sizes.
  • Error Handling: The DECLARATIVES section is used for error management.

COBOL's syntax may seem verbose, but it was designed for clarity and readability, making it highly suitable for business logic and handling large volumes of data processing.