Thread: stack overflow |c|

hi,
my problem is when i press m or M (min or max) and input negetive numbers (like -88, -6...)
i get stack overflow
im asking why???

Code:

#include <stdio.h>
#include <math.h>
#include <string.h>


int gcd(int, int);


int main()
{
	int x, y, result, power, user_quit = 1;
	char c;
	while (user_quit)
	{
		printf("please enter char and 2 integers: ");
		_flushall();
		c = getchar();


		if ((c == 'q') || (c == 'Q'))
		{
			printf("finish!");
			user_quit = 0;
			getchar();
		}
		else
		{
			scanf("%d%d", &x, &y);
			int min = (x < y ? x : y);
			int max = (x > y ? x : y);
			result = gcd(x, y);
			power = (double)pow(x, y);


			switch (c)
			{
			case 'A':
			case 'a':
				printf("The Average of %d and %d is: %d.\n", x, y, (x + y) / 2);
				break;
			case '*':
				printf("The Multiply of %d and %d is: %d.\n", x, y, x*y);
				break;
			case 'm':
				printf("The Minimum of %d and %d is: %d.\n", x, y, min);
				break;
			case 'M':
				printf("The Maximum of %d and %d is: %d.\n", x, y, max);
				break;
			case 'G':
				printf("The GCD of %d and %d is: %d.\n", x, y, result);
				break;
			case '^':
				printf("The Power of %d and %d is: %lf.\n", x, y,(double) power);
				break;
			default: printf("illegal\n");


			}
		}
	}
	getchar();
	return 0;
}


int gcd(int x, int y)


{
	while (x != y)
	{
		if (x > y)
		{
			return gcd(x - y, y);
		}
		else
		{
			return gcd(x, y - x);
		}
	}
	return x;
}

You're getting a stack overflow because gcd(), a recursive function, gets called repeatedly and never returns for -ve numbers.
I'd suggest you first do this the old fashioned way i.e. using paper and pencil to see the program flow before translating it into C.