Functions in C

Introduction

A function in C is a block of code that performs a specific task. Functions improve modularity, readability, and reusability of programs. Instead of writing the same code repeatedly, a function can be called multiple times.

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Key Points

1. Function Definition

• Syntax: returnType functionName(parameters) { // code }
• Example: int add(int a, int b) { return a + b; }

2. Function Declaration (Prototype)

• Tells the compiler about the function’s name, return type, and parameters before main function.
• Syntax: int add(int, int);

3. Function Call

• Executes the function.
• Example: int result = add(5, 3);

4. Types of Functions

1. Built-in functions – Provided by C standard library, e.g., printf(), scanf(), sqrt()
2. User-defined functions – Created by programmer to perform specific tasks

5. Function Return Types

• void → Does not return any value
• Non-void → Returns a value (int, float, char, etc.)

6. Advantages

• Modular programming: Divide program into manageable sections
• Reusability: Use same function in multiple programs
• Easier debugging: Fix errors in one place

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Example Code

#include <stdio.h>

// Function declaration
int add(int a, int b);

int main() {
    int sum;
    sum = add(10, 5); // Function call
    printf("Sum: %d", sum);
    return 0;
}

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