Exchanging 2 integer's value, exclude 3. integer (in C programming)

Hi, the question is simple but the answer isnt.)
Exchange 2 integer's value except the third integer.For ex, x=10, y=20 we have to make x=20 and y=10 but we banned to use a 3. integer like integer z. I use pointers for it.

#include <stdio.h>
#include <stdlib.h>
int main(){
int *p,*q,x=10,y=20; //first values
*q=x;
*p=y;
x=*q;
y=*p;	
printf("new x %d and y %d",x,y); //final values
system("PAUSE");
return 0;
}

Code (markup):

Help me solving either finding a way.

 

Much easier:

void main()

{

int a,b;

clrscr();

printf("\n\n\t\tenter any two nos...");

scanf("%d%d",&a,&b);

a=a+b;

b=a-b;

a=a-b;

printf("\n\n\t\tvalue of a=",a);

printf("\n\n\t\tvalue of b=",b);

getch();

} 

Code (markup):

 

Do not use any temp variable or pointer. Use XOR '^' operation to do that for you.

y = x ^ y;
x = y ^ x;
y = x ^ y;


regards

 

That is rediculous Imtiger47... lol