**C Program to Find Factorial of a Number:**

The factorial of a positive integer n is equal to 1*2*3*…n. You will learn to calculate the factorial of a number using for loop in this example.

The factorial of a positive number n is given by:

factorial of n (n!) = 1*2*3*4....n

The factorial of a negative number doesn’t exist. And, the factorial of 0 is 1, `0! = 1`

## Example: Factorial of a Number

#include <stdio.h> int main() { int n, i; unsigned long long factorial = 1; printf("Enter an integer: "); scanf("%d",&n); // show error if the user enters a negative integer if (n < 0) printf("Error! Factorial of a negative number doesn't exist."); else { for(i=1; i<=n; ++i) { factorial *= i; // factorial = factorial*i; } printf("Factorial of %d = %llu", n, factorial); } return 0; }

**Output**

Enter an integer: 10 Factorial of 10 = 3628800

This program takes a positive integer from the user and computes factorial using for loop.

Since the factorial of a number may be very large, the type of `factorial` variable is declared as `unsigned long long`

.

If the user enters negative number, the program displays error message.

**C Program to Find Factorial of a Number Using Recursion:**

Example to find factorial of a non-negative integer (entered by the user) using recursion.

#include <stdio.h> long int multiplyNumbers(int n); int main() { int n; printf("Enter a positive integer: "); scanf("%d", &n); printf("Factorial of %d = %ld", n, multiplyNumbers(n)); return 0; } long int multiplyNumbers(int n) { if (n >= 1) return n*multiplyNumbers(n-1); else return 1; }

**Output**

Enter a positive integer: 6 Factorial of 6 = 720