Lesson 21: Introduction to Functions

Functions are blocks of code designed to perform a specific task. They promote modularity, reusability, and readability.

Components of a Function

1. Function Declaration (Prototype)

This tells the compiler about the function's name, return type, and parameters before it is used. Often placed in a header file or at the top of the source file.

Syntax: return_type function_name(parameter_list);

c int add(int a, int b); // Prototype

2. Function Definition

The actual code block that implements the function's logic.

c int add(int a, int b) { // Definition header int sum = a + b; return sum; // Returns an integer value }

3. Function Call

Executing the function by using its name and providing arguments.

c #include <stdio.h>

// 1. Declaration int add(int a, int b);

int main() { int result; // 3. Function Call result = add(10, 5); printf("The sum is: %d\n", result); return 0; }

// 2. Definition int add(int a, int b) { return a + b; }

Note: If the function definition appears before main(), a separate prototype might not be necessary, but prototypes are essential for multi-file programs.