Factorial Program in C Using Recursion – Simple Code with Explanation

When learning programming, one of the most common beginner tasks is writing a factorial program in C. In this post, you’ll learn how to find the factorial of a number using recursion, one of the most important concepts in C programming.

What is a Factorial?

The factorial of a number n is the product of all positive integers less than or equal to n. It’s denoted as n!.

For example:

5! = 5 × 4 × 3 × 2 × 1 = 120

Why Use Recursion?

Recursion is a technique where a function calls itself to solve a smaller part of the problem. It’s ideal for problems that can be broken into similar subproblems, like factorials.

Factorial Program in C Using Recursion

Here’s a simple and clear C program using recursion to find the factorial of a number:

#include <stdio.h>

// Recursive function to find factorial
int factorial(int n) {
    if (n == 0 || n == 1)
        return 1; // Base case
    else
        return n * factorial(n - 1); // Recursive call
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);

    if (num < 0)
        printf("Factorial is not defined for negative numbers.\n");
    else
        printf("Factorial of %d is %d\n", num, factorial(num));

    return 0;
}

Explanation

• If n is 0 or 1, the factorial is 1 (base case).
• Otherwise, the function calls itself with n-1 and multiplies it by n.
• This continues until it reaches the base case.

Sample Output

Enter a number: 5
Factorial of 5 is 120

When to Use Recursion for Factorials?

Use recursion:

• For educational or demonstration purposes
• When writing short, elegant code

Avoid recursion:

• When performance is critical (use iteration instead to avoid stack overflow for large numbers)

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Final Thoughts

The factorial program in C using recursion is an excellent example to understand how recursive functions work. It’s also a key building block for learning advanced topics like backtracking, divide-and-conquer, and data structures.