#include <stdio.h>

int fact(int n)
{
	if (n == 0)
		return 1;
	else
		return n * fact(n - 1);
}

int main(void)
{
	int n;
	printf("To calculate the factorial of a given number\n\n");
	printf("Enter a number: ");
	scanf("%d", &n);
	if (n < 0) {
		printf("Invalid input, must be greater than -1\n");
		return 0;
	}
	printf("%d! = %d\n", n, fact(n));
	return 0;
}

/*
Output:
Set 1:
To calculate the factorial of a given number

Enter a number: -1
Invalid input, must be greater than zero

Set 2:
To calculate the factorial of a given number

Enter a number: 0
0! = 1

Set 3:
To calculate the factorial of a given number

Enter a number: 5
5! = 120

Set 4:
To calculate the factorial of a given number

Enter a number: 10
10! = 3628800

*/