Functions

As programs become larger, writing all the code inside main() can make the program difficult to understand and maintain.

Functions help us divide a large program into smaller, reusable pieces.

What is a Function?

A function is a block of code designed to perform a specific task.

For example, instead of writing the same addition code multiple times, we can create a function for it and call that function whenever we need it.

void greet()
{
    printf("Hello!");
}

We can call it using:

greet();

Why Use Functions?

Functions make programs:

• Easier to understand

• Reusable

• Easier to test and debug

• Better organized

For example, a large program could be divided into:

main()
 ├── calculateTotal()
 ├── checkResult()
 └── displayResult()

Each function handles a specific task.

Creating a Function

A basic function looks like this:

return_type function_name()
{
    // code
}

For example:

void greet()
{
    printf("Hello, John!");
}

Here:

• void → return type

• greet → function name

• () → parameters

• { } → function body

Calling a Function

Creating a function doesn't execute it. We need to call it.

#include <stdio.h>

void greet()
{
    printf("Hello, John!");
}

int main()
{
    greet();

    return 0;
}

Output:

Hello, John!

When greet() is called, the code inside the function executes.

Function with Parameters

A function can receive values from the caller. These values are called parameters.

void greet(char name[])
{
    printf("Hello, %s!", name);
}

We can call it like this:

greet("John");

The function receives "John" and uses it inside the function.

Function with a Return Value

A function can also calculate something and return a value.

For example:

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

Now we can use it:

int result = add(10, 20);

printf("%d", result);

Output:

30

Here, int indicates that the function returns an integer.

Four Common Types of Functions

Functions can be classified based on whether they take parameters and return a value.

The last type is very common:

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

Function Declaration

Sometimes we call a function before its actual definition. In that case, we can declare it first.

int add(int, int);

int main()
{
    printf("%d", add(10, 20));

    return 0;
}

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

The first line is called a function declaration or prototype.

In Simple Words

A function is a reusable block of code that performs a specific task.

Instead of putting everything inside main(), we can divide our program into smaller functions.

For example:

       Program
          ↓
   ┌──────┼──────┐
   ↓      ↓      ↓
 input  calculate output

This makes our C programs cleaner, easier to manage, and reusable.