C Program to find factorial of a number

In mathematics, the factorial of a positive integer n, denoted by n!, is the product of all positive integers less than or equal to n:

n! = n x (n-1) x (n-2) x (n-3) x ... x 3 x 2 x 1.

For example:

6! = 6*5*4*3*2*1 = 720

And the value of 0! is 1.

This is the most common question asked in Technical interview or Coding round.

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There are many ways to solve this question some of them are discussed here:

Recursive implementation using C:

#include<stdio.h>

int factorial(int n)
{
    if(n == 0)
        return 1;
    return n * factorial(n-1);
}
int main()
{
    int number;
    printf("Enter number : \n");
    scanf("%d",&number);
    printf("Factorial of %d is %d ",number,factorial(number));
    return 0;
}

Output:
Enter number :
5
Factorial of 5 is 120

Iterative Implementation using C:

#include<stdio.h>

int factorial(int n)
{
    if(n == 0 || n == 1)
       return 1;
    int fact=1, i;
    for(i=2; i<=n; i++)
    {
       fact = fact * i;
    } 
    return fact;
}
int main()
{
   int number;
   printf("Enter number : \n");
   scanf("%d",&number);
   printf("Factorial of %d is %d ",number,factorial(number));
   return 0;
}

Output:
Enter number :
5
Factorial of 5 is 120

Using ternary operator in C:

#include<stdio.h>

int factorial(int n)
{
    return (n == 1 || n == 0 ) ? 1 : n * factorial(n - 1);
}
int main()
{
    int number;
    printf("Enter number :\n");
    scanf("%d",&number);
    printf("Factorial of %d is %d ",number,factorial(number));
    return 0;   
}

Output:
Enter number :
5
Factorial of 5 is 120

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