Functions in C

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A function is a block of code that performs a specific task.
Functions help in modular programming, code reuse, and readability.

Types of Functions

1. Library Functions

2. User-Defined Functions

1. Library Functions

Predefined functions provided by C libraries.

Examples:

• printf()

• scanf()

• strlen()

• sqrt()

2. User-Defined Functions

Functions written by the programmer.

Structure of a Function

Function Declaration (Prototype)

return_type function_name(parameter_list);

Function Definition

return_type function_name(parameter_list) {
    statements;
}

Function Call

function_name(arguments);

Example Program

#include 

int add(int a, int b) {
    return a + b;
}

int main() {
    int sum;
    sum = add(5, 3);
    printf("Sum = %d", sum);
    return 0;
}

Components of a Function

• Return type – Type of value returned

• Function name – Identifier

• Parameters – Values passed to function

• Function body – Statements to execute

Types of User-Defined Functions

Based on arguments and return value:

1. No arguments, no return value

2. Arguments, no return value

3. No arguments, return value

4. Arguments and return value

Call by Value

• Actual value is passed to function

• Changes do not affect original variable

Recursion

A function calling itself.

int fact(int n) {
    if (n == 0)
        return 1;
    else
        return n * fact(n - 1);
}

Advantages of Functions

• Code reusability

• Easy debugging

• Better readability

• Reduced program size

Summary

• Functions divide a program into modules

• main() is the starting function

• Functions can return values

• Recursion is supported