OJ Board

HELP!!why WA?I have already tried many cases and the answer is correct.

#include <stdio.h>

int main(void)
{
unsigned int a, b;
int carry, c, mod1, mod2;
while(1)
{
scanf("%u %u",&a, &b);
carry = 0;
if(a == 0 && b == 0)
{
break;
}
if(b > a)
{
a = a^b;
b = a^b;
a = a^b;
}
while(a ...