How to use find out the factorial of a number in C language

#include <stdio.h>
long int factorial(int n);
int main()
{
    int num;
    printf("Enter a Number : ");
    scanf("%d",&num);
    if(num<0)
    printf("No Factorial of Negative Number\n");
    else 
    printf("Factorial of %d is %ld\n",num,factorial(num));
    return 0;
} 
long int factorial(int n)
{
    int i;
    long int fact=1;
    if(n==0){
           return 1;
    }
    for(i=n; i>1; i--){
        fact*=i;
    }
    return fact;
}

Enter a number : 8
Factorial of 8 is 40320