C Program to Find Factorial of a Number

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

#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