Recursion is a programming technique in which a function calls itself to solve a problem. A recursive function repeatedly calls itself until a base condition is met. Without a base condition, the recursion continues indefinitely and may cause a stack overflow.

Syntax

return_type function_name(parameters)
{
    if (base_condition)
        return value;
    else
        return function_name(modified_parameters);
}

Components of Recursion

1. Base Case – Stops the recursive calls.
2. Recursive Case – The function calls itself with modified arguments.

Example 1: Factorial Using Recursion

The factorial of a number is:

• 5! = 5 × 4 × 3 × 2 × 1 = 120
• 0! = 1

Program

#include <stdio.h>

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

int main()
{
    int num = 5;

    printf("Factorial of %d = %d", num, factorial(num));

    return 0;
}

Output

Factorial of 5 = 120

Working

factorial(5)
= 5 × factorial(4)
= 5 × 4 × factorial(3)
= 5 × 4 × 3 × factorial(2)
= 5 × 4 × 3 × 2 × factorial(1)
= 120

Example 2: Fibonacci Series Using Recursion

Program

#include <stdio.h>

int sum(int n)
{
    if (n == 1)
        return 1;
    else
        return n + sum(n - 1);
}

int main()
{
    int n = 5;

    printf("Sum = %d", sum(n));

    return 0;
}

Output

Fibonacci Series:0 1 1 2 3 5 8 13 21 34

Advantages of Recursion

• Makes code shorter and easier to understand.
• Suitable for problems that can be divided into smaller subproblems.
• Useful for tree and graph traversal, factorial, Fibonacci, and divide-and-conquer algorithms.

Disadvantages of Recursion

• Uses more memory due to function call stack.
• Can be slower than iterative solutions.
• Incorrect or missing base case can lead to infinite recursion and stack overflow.

Difference Between Recursion and Iteration

Key Point

A recursive function must always have a base case to terminate the recursion. Without it, the function will keep calling itself until the program crashes due to a stack overflow.