/*
 * Simple example of recursive function.
 */
#include <stdio.h>

int factorial(int n); /* function declaration */

int main(void) {

	int x;

	printf("enter integer\n");
	if (scanf("%d", &x) != 1) {
		printf("bad input\n");
		return 1; /* nonzero return means error */
	}
	printf("x %d, fac x %d\n", x, factorial(x));
	return 0;
}

/*
 * n! = n * (n-1) * (n-2) * ... * 1
 *
 * n! =
 *   if n == 0, 1
 *   otherwise n * (n-1)!
 */
int factorial(int n) {
	if (n <= 0) {
		return 1;
	}
	else {
		return n * factorial(n-1);
	}
}