COBOL Tutorial

COBOL FUNCTION-ID Clause - Quick Reference

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Overview

The FUNCTION-ID clause is used in COBOL to define functions that can accept parameters and return values. This clause enables functional programming capabilities in COBOL, allowing for modular, reusable code components.

Purpose and Usage

Function definition - Define reusable function components
Parameter passing - Accept input parameters using USING clause
Return values - Return data using RETURNING clause
Modular programming - Create self-contained code units
Functional programming - Enable function-based programming style

Function Structure

FUNCTION-ID function-name

USING parameter1, parameter2, ...

RETURNING result

PROCEDURE DIVISION

... function logic ...

GOBACK

END FUNCTION

Functions have a defined structure with parameters, return values, and logic.

Syntax

The FUNCTION-ID clause follows specific syntax patterns for defining functions with parameters and return values.

Basic Syntax

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* Basic FUNCTION-ID clause syntax
FUNCTION-ID function-name
    [USING parameter1, parameter2, ...]
    [RETURNING result-data-name]
    [ENVIRONMENT DIVISION]
    [DATA DIVISION]
    [PROCEDURE DIVISION]
END FUNCTION function-name.
 
* Examples
FUNCTION-ID ADD-NUMBERS
    USING PARAM1 PARAM2
    RETURNING RESULT.
 
FUNCTION-ID CALCULATE-TOTAL
    USING AMOUNT TAX-RATE
    RETURNING TOTAL-AMOUNT.
 
FUNCTION-ID VALIDATE-DATE
    USING DATE-STRING
    RETURNING IS-VALID.
 
* Complete example
FUNCTION-ID CALCULATE-INTEREST
    USING PRINCIPAL-AMOUNT INTEREST-RATE YEARS
    RETURNING INTEREST-AMOUNT.
 
DATA DIVISION.
LINKAGE SECTION.
01  PRINCIPAL-AMOUNT    PIC 9(8)V99.
01  INTEREST-RATE       PIC 9(3)V99.
01  YEARS              PIC 9(2).
01  INTEREST-AMOUNT     PIC 9(8)V99.
 
PROCEDURE DIVISION USING PRINCIPAL-AMOUNT INTEREST-RATE YEARS
    RETURNING INTEREST-AMOUNT.
    COMPUTE INTEREST-AMOUNT = PRINCIPAL-AMOUNT * INTEREST-RATE * YEARS
    GOBACK.
END FUNCTION CALCULATE-INTEREST.

FUNCTION-ID defines the function name and characteristics.

Parameter Definition

Clause	Purpose	Example
USING	Define input parameters	USING PARAM1 PARAM2
RETURNING	Define return value	RETURNING RESULT
LINKAGE SECTION	Define parameter data types	01 PARAM1 PIC 9(5)
PROCEDURE DIVISION	Define function logic	Function implementation

Function Call Syntax

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* Calling functions
FUNCTION function-name(parameter1, parameter2, ...)
 
* Examples
FUNCTION ADD-NUMBERS(100, 200)
 
COMPUTE RESULT = FUNCTION CALCULATE-TOTAL(AMOUNT, TAX-RATE)
 
IF FUNCTION VALIDATE-DATE(DATE-STRING) = 'Y'
    DISPLAY 'Valid date'
END-IF
 
* Using in expressions
COMPUTE TOTAL = FUNCTION ADD-NUMBERS(A, B) + FUNCTION ADD-NUMBERS(C, D)
 
* Storing function result
MOVE FUNCTION CALCULATE-INTEREST(PRINCIPAL, RATE, YEARS) TO INTEREST

Functions are called using the FUNCTION keyword with parameters.

Common Use Cases

FUNCTION-ID is commonly used in specific scenarios where modular, reusable code components are needed.

Mathematical Calculations

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* Mathematical function example
FUNCTION-ID CALCULATE-AREA
    USING LENGTH WIDTH
    RETURNING AREA.
 
DATA DIVISION.
LINKAGE SECTION.
01  LENGTH              PIC 9(5)V99.
01  WIDTH               PIC 9(5)V99.
01  AREA                PIC 9(8)V99.
 
PROCEDURE DIVISION USING LENGTH WIDTH
    RETURNING AREA.
    COMPUTE AREA = LENGTH * WIDTH
    GOBACK.
END FUNCTION CALCULATE-AREA.
 
* Usage
COMPUTE RECTANGLE-AREA = FUNCTION CALCULATE-AREA(10.5, 5.2)
DISPLAY 'Area: ' RECTANGLE-AREA

Functions are ideal for mathematical calculations and formulas.

Data Validation

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* Data validation function
FUNCTION-ID VALIDATE-EMAIL
    USING EMAIL-ADDRESS
    RETURNING IS-VALID.
 
DATA DIVISION.
LINKAGE SECTION.
01  EMAIL-ADDRESS       PIC X(50).
01  IS-VALID           PIC X.
 
PROCEDURE DIVISION USING EMAIL-ADDRESS
    RETURNING IS-VALID.
    IF EMAIL-ADDRESS CONTAINS '@' AND EMAIL-ADDRESS CONTAINS '.'
        MOVE 'Y' TO IS-VALID
    ELSE
        MOVE 'N' TO IS-VALID
    END-IF
    GOBACK.
END FUNCTION VALIDATE-EMAIL.
 
* Usage
IF FUNCTION VALIDATE-EMAIL(USER-EMAIL) = 'Y'
    DISPLAY 'Valid email address'
ELSE
    DISPLAY 'Invalid email address'
END-IF

Functions provide reusable validation logic.

String Manipulation

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* String manipulation function
FUNCTION-ID REVERSE-STRING
    USING INPUT-STRING
    RETURNING REVERSED-STRING.
 
DATA DIVISION.
LINKAGE SECTION.
01  INPUT-STRING        PIC X(50).
01  REVERSED-STRING     PIC X(50).
 
WORKING-STORAGE SECTION.
01  STRING-LENGTH       PIC 9(2).
01  COUNTER             PIC 9(2).
01  TEMP-CHAR           PIC X.
 
PROCEDURE DIVISION USING INPUT-STRING
    RETURNING REVERSED-STRING.
    MOVE INPUT-STRING TO REVERSED-STRING
    INSPECT REVERSED-STRING TALLYING STRING-LENGTH FOR CHARACTERS
    PERFORM VARYING COUNTER FROM 1 BY 1 UNTIL COUNTER > STRING-LENGTH / 2
        MOVE REVERSED-STRING(COUNTER:1) TO TEMP-CHAR
        MOVE REVERSED-STRING(STRING-LENGTH - COUNTER + 1:1) 
            TO REVERSED-STRING(COUNTER:1)
        MOVE TEMP-CHAR TO REVERSED-STRING(STRING-LENGTH - COUNTER + 1:1)
    END-PERFORM
    GOBACK.
END FUNCTION REVERSE-STRING.
 
* Usage
MOVE FUNCTION REVERSE-STRING('HELLO') TO REVERSED-WORD
DISPLAY 'Reversed: ' REVERSED-WORD

Functions enable complex string manipulation operations.

Best Practices and Tips

Following these best practices ensures effective use of the FUNCTION-ID clause for functional programming.

FUNCTION-ID Design Principles

Single responsibility - Each function should have one clear purpose
Clear naming - Use descriptive function names
Parameter validation - Validate input parameters
Return value consistency - Ensure consistent return value types
Documentation - Document function purpose and parameters
Error handling - Handle errors gracefully within functions

Common Pitfalls to Avoid

Pitfall	Problem	Solution
Complex functions	Hard to understand and maintain	Keep functions simple and focused
No parameter validation	Incorrect results or errors	Always validate input parameters
Inconsistent return types	Confusing and error-prone	Use consistent return value types
Poor naming	Hard to understand function purpose	Use descriptive function names
No error handling	Functions fail without proper error messages	Implement proper error handling

Performance Considerations

Function call overhead - Function calls have some overhead
Parameter passing cost - Parameter passing adds processing time
Return value handling - Return value processing has overhead
Memory usage - Functions may use additional memory
Optimization opportunities - Some compilers optimize function calls
Inline vs function calls - Consider when to use inline code vs functions

When to Use FUNCTION-ID

Use Case	FUNCTION-ID Suitability	Reasoning
Reusable logic	Excellent	Perfect for code that needs to be reused
Complex calculations	Excellent	Ideal for complex business logic
Data validation	Good	Good for validation rules
Simple operations	Poor	Overkill for simple operations
Performance-critical code	Poor	Function call overhead may be too high

FUNCTION-ID Clause Quick Reference

Usage	Syntax	Example
Basic function	FUNCTION-ID function-name	FUNCTION-ID CALCULATE-TOTAL
Function with parameters	FUNCTION-ID function-name USING params	FUNCTION-ID ADD-NUMBERS USING PARAM1 PARAM2
Function with return	FUNCTION-ID function-name RETURNING result	FUNCTION-ID CALCULATE-TOTAL RETURNING RESULT
Function call	FUNCTION function-name(params)	FUNCTION ADD-NUMBERS(100, 200)
Function in expression	COMPUTE result = FUNCTION function-name(params)	COMPUTE TOTAL = FUNCTION ADD-NUMBERS(A, B)

Test Your Knowledge

1. What is the primary purpose of the FUNCTION-ID clause in COBOL?

To define data types
To define function names and characteristics in functional programming
To control file operations
To perform calculations

2. Which clause is used to specify the return type of a function?

USING
RETURNING
FUNCTION-ID
END FUNCTION

3. What is the correct syntax for defining a function parameter?

USING parameter-name PIC X(10)
PARAMETER parameter-name PIC X(10)
INPUT parameter-name PIC X(10)
ARGUMENT parameter-name PIC X(10)

4. How do you return a value from a function in COBOL?

Use the RETURN statement with a value
Use the GOBACK statement with a value
Use the EXIT statement with a value
Use the STOP statement with a value

5. What is the relationship between FUNCTION-ID and PROGRAM-ID?

They are the same thing
FUNCTION-ID defines functions while PROGRAM-ID defines main programs
FUNCTION-ID is obsolete and PROGRAM-ID should be used instead
They cannot be used together

COBOL Tutorial

COBOL FUNCTION-ID Clause - Quick Reference

Overview

Purpose and Usage

Function Structure

Syntax

Basic Syntax

Parameter Definition

Function Call Syntax

Common Use Cases

Mathematical Calculations

Data Validation

String Manipulation

Best Practices and Tips

FUNCTION-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use FUNCTION-ID

FUNCTION-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Related Concepts

PROGRAM-ID Clause

FUNCTION Statement

Functional Programming

Parameter Passing

Return Values

Related Pages

COBOL Tutorial

COBOL FUNCTION-ID Clause - Quick Reference

Overview

Purpose and Usage

Function Structure

Syntax

Basic Syntax

Parameter Definition

Function Call Syntax

Common Use Cases

Mathematical Calculations

Data Validation

String Manipulation

Best Practices and Tips

FUNCTION-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use FUNCTION-ID

FUNCTION-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Can a function have multiple return types?

What is the difference between a function and a paragraph?

Can functions call other functions?

Are functions supported in all COBOL dialects?

How do you handle errors in functions?

Related Concepts

PROGRAM-ID Clause

FUNCTION Statement

Functional Programming

Parameter Passing

Return Values

Related Pages