Factorial Program in C

A factorial is the product of all the natural numbers less than or equal to the given number n. For Example, the factorial of 6 is 6 * 5 * 4 * 3 * 2 * 1 which is 720. In this article, we will explore a few programs to find the factorial of a number in C.

factorial in c

We can write the factorial program in C using two methods:

Using Loops
Using Recursion

1. Factorial Program using for Loop

In this method, we use a loop that runs (n – 1) times to get the product of all numbers starting from 1 to n. The below C program use for loop to find the factorial.

C

// C program to implement the above approach
#include <stdio.h>
 
// Function to find factorial of given number
unsigned int factorial(unsigned int n)
{
    int result = 1, i;
 
    // loop from 2 to n to get the factorial
    for (i = 2; i <= n; i++) {
        result *= i;
    }
 
    return result;
}
 
// Driver code
int main()
{
    int num = 5;
    printf("Factorial of %d is %d", num, factorial(num));
    return 0;
}

Output

Factorial of 5 is 120

Time Complexity: O(n)
Auxiliary Space: O(1)

2. Factorial Program using Recursion

In this method, we find the factorial in C using a recursive function. This recursive function will call itself n number of times and each time, the value of n will be decreased by 1. The recursion will stop when n = 1.

C

// C program to find factorial of given number
#include <stdio.h>
 
// Function to find factorial of given number
unsigned int factorial(unsigned int n)
{
    if (n == 1) {
      return 1;
    }
   
    return n * factorial(n - 1);
}
 
// Driver code
int main()
{
    int num = 5;
    printf("Factorial of %d is %d", num, factorial(num));
    return 0;
}