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

int main(void) {

	int n;
	int counter;
	int n_factorial;

	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("\ncomputing using while loop:\n");
		n_factorial = n;
		counter = n-1;
		while (counter >= 2) {
			n_factorial *= counter;
			counter -= 1;
		}
		printf("%d factorial is %d\n", n, n_factorial);

		printf("\ncomputing using for loop:\n");
		n_factorial = n;
		for (counter = n-1; counter >= 2; counter -= 1) {
			n_factorial *= counter;
		}
		printf("%d factorial is %d\n", n, n_factorial);
	}
	return 0;
}