Introduction to COBOL

• COBOL (Common Business-Oriented Language) is a compiled English-like computer programming language designed for business use

COBOL Key Features

• COBOL is primarily used in business, finance, and administrative systems for companies and governments
• It is a procedural, imperative, and, since 2002, object-oriented language
• COBOL is known for its readability due to its English-like syntax, which simplifies program maintenance
• The language supports large-scale data processing and is suitable for batch-oriented tasks
• COBOL's strengths include file handling, report generation, and sequential processing
• COBOL is still widely used because many legacy systems critical to businesses rely on it

COBOL Program Structure

• A COBOL program is divided into four divisions
• These divisions must be present in the following order: Identification Division, Environment Division, Data Division, and Procedure Division
• Each division serves a specific purpose within the program structure

Identification Division

• The Identification Division provides metadata about the program
• It includes the program's name, author, and other documentation details
• This division is primarily for documentation and does not affect the program's execution
• The basic structure includes the division header followed by a PROGRAM-ID paragraph, which specifies the program's name
• Optionally, other paragraphs like AUTHOR, INSTALLATION, DATE-WRITTEN, and SECURITY can be included for additional documentation

Environment Division

• The Environment Division describes the hardware and software environment in which the program will run
• It is divided into two sections: Configuration Section and Input-Output Section
• The Configuration Section deals with the computer's characteristics, such as the source and object computers
• The Input-Output Section defines file-related information, such as file assignments and organization
• The FILE-CONTROL paragraph associates files with physical devices, and the I-O-CONTROL paragraph manages buffer and memory allocation

Data Division

• The Data Division describes the data the program will use
• It is divided into several sections, including the File Section, Working-Storage Section, Local-Storage Section, and Linkage Section
• The File Section describes the format and structure of the files used by the program
• The Working-Storage Section defines variables and data structures used for temporary storage and data manipulation
• The Local-Storage Section is similar to the Working-Storage Section but allocates memory on a per-call basis
• The Linkage Section describes data passed to the program from other programs

Procedure Division

• The Procedure Division contains the executable instructions of the program
• It is where the program's logic is defined, including data manipulation, calculations, and input/output operations
• This division is organized into sections and paragraphs, with each paragraph containing one or more statements
• COBOL statements are typically written in a structured, English-like syntax
• The Procedure Division uses verbs like MOVE, ADD, SUBTRACT, MULTIPLY, DIVIDE, IF, PERFORM, and DISPLAY to perform operations

COBOL Syntax Elements

• COBOL syntax includes several basic elements: words, literals, PICTURE clauses, and statements
• Words are user-defined or reserved, forming the basis of COBOL syntax
• Literals are constant values, such as numeric values or character strings
• PICTURE clauses define the format and characteristics of data fields, such as length and data type
• Statements are instructions that perform specific actions

COBOL Verbs

• COBOL uses verbs to perform operations
• Common verbs include:
  • MOVE: Transfers data from one field to another
  • ADD: Adds two or more numeric values
  • SUBTRACT: Subtracts one numeric value from another
  • MULTIPLY: Multiplies two numeric values
  • DIVIDE: Divides one numeric value by another
  • DISPLAY: Outputs data to the console or a file
  • IF: Executes a block of code based on a condition
  • PERFORM: Executes a paragraph or section of code, often used for looping and modularization

Data Types and PICTURE Clauses

• COBOL supports various data types, including numeric, alphanumeric, and alphabetic
• PICTURE clauses define the format and characteristics of data fields
• Numeric fields use '9' to represent digits, 'V' to indicate the position of the decimal point, and 'S' for the sign
• Alphanumeric fields use 'X' to represent any character
• Alphabetic fields use 'A' to represent letters
• Examples of PICTURE clauses include:
  • PIC 9(5) for a 5-digit numeric field
  • PIC 9(3)V99 for a numeric field with 3 digits before and 2 digits after the decimal point
  • PIC X(20) for a 20-character alphanumeric field

File Handling in COBOL

• COBOL excels at file handling, supporting sequential, indexed, and relative file organizations
• The FILE-CONTROL paragraph in the Environment Division defines file attributes
• The OPEN statement opens a file for input, output, or I/O
• The READ statement reads a record from a file
• The WRITE statement writes a record to a file
• The REWRITE statement updates a record in a file
• The CLOSE statement closes a file

Example COBOL Program Snippet

• IDENTIFICATION DIVISION.
• PROGRAM-ID. HELLO-WORLD.
• DATA DIVISION.
• WORKING-STORAGE SECTION.
• 01 WS-MESSAGE PIC X(13) VALUE 'Hello, World!'.
• PROCEDURE DIVISION.
• DISPLAY WS-MESSAGE.
• STOP RUN.
• This program displays "Hello, World!" to the console, demonstrating a simple COBOL structure

COBOL Coding Standards

• Adhering to coding standards improves readability and maintainability
• Use meaningful data names to enhance clarity
• Comment code to explain logic and functionality
• Indent code blocks to improve structure
• Use modular design to break down complex tasks into smaller, manageable units
• Keep lines of code to a manageable length
• Group related data items together in data structures

Compilation and Execution

• COBOL programs must be compiled before they can be executed
• The compilation process translates the COBOL source code into machine-executable code
• Compilers are specific to the operating system and hardware platform
• After compilation, the program can be executed, performing the tasks defined in the Procedure Division
• COBOL programs are often run in batch mode for large-scale data processing tasks