How to write an algorithm to detect if two integers have opposite signs ?

/* detect if two integers have opposite signs */
#include <stdio.h>

int x , y;
typedef int bool;
bool f;

int sdetect(x , y)
{

f = ((x ^ y) < 0);

if ( f == 1 ) {
printf("They have opposite signs\n");
}
else
{
printf("They have same signs\n");
}

}