factorial-iterative-with-overflow-detection.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <float.h>

unsigned long long factorial(unsigned num)
{
	unsigned int i = 1;
	unsigned long long result = 1;
	for (; i <= num; ++i)
		{
			if (result > ULLONG_MAX / i)
				{
					return 0;
				}

			result = result * i;
		}

	return result;
}

int factorial_rosetta(int n) {
    int result = 1;
    for (int i = 1; i <= n; ++i)
	    {
		    result *= i;
		    printf("result now: %d\n", result);
	    }
    return result;
}

int main(void)
{
	unsigned long long res = factorial(10);
	if (res == 0)
		{
			puts("factorial(10) == Overflow");
		}
	else
		{
			printf("factorial(10) == %llu\n", res);
		}

	res = factorial(13);
	if (res == 0)
		{
			puts("factorial(13) == Overflow");
		}
	else
		{
			printf("factorial(13) == %llu\n", res);
		}

	res = factorial(20);
	if (res == 0)
		{
			puts("factorial(200) == Overflow");
		}
	else
		{
			printf("factorial(20) == %llu\n", res);
		}

	res = factorial(21);
	if (res == 0)
		{
			puts("factorial(21) == Overflow");
		}
	else
		{
			printf("factorial(21) == %llu\n", res);
		}

	res = factorial(5000);
	if (res == 0)
		{
			puts("factorial(5000) == Overflow");
		}
	else
		{
			printf("factorial(5000) == %llu\n", res);
		}

	return EXIT_SUCCESS;
}