/*
 * Program demonstrating use of recursion to compute factorial of a number.
 *
 * Input:  a positive integer n.
 *
 * Output:  n! 
 */
#include <stdio.h>

/* Compute n! and return it */
int factorial(int n) {
	int result;
	if (n <= 1) {
		result = 1;
	}
	else {
		result = n * factorial(n-1);
	}
	return result;
}

/* Main program */
int main(void) {

	int n;

	printf("enter a positive integer:\n");

	if (scanf("%d", &n) !=1 ) {
		printf("error:  not an integer\n");
	}
	else if (n <= 0) {
		printf("error:  negative or 0\n");
	}
	else {
		printf("%d factorial is %d\n", n, factorial(n));
	}
	return 0;
}