/*
 * Program to compute factorial using recursion.
 */
#include <stdio.h>

int factorial(int n);

int main(void) {

	int n;
	printf("enter n\n");
	if (scanf("%d", &n) != 1) {
		printf("not number\n");
		return 1;
	}
	if (n < 0) {
		printf("negative\n");
		return 1;
	}
	printf("factorial(%d) is %d\n", n, factorial(n));

	return 0;
}

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