pointer swap

#include<stdio.h>
void swap(int *x,int *y)
{
 int t;
 t=*x;
 *x=*y;
 *y=t;


}
int main()
{ int a=20,b=30;
a=a+b;
b=a-b;
a=a-b;
   printf("value before swap : %d %d\n \n",a,b);
   swap(&a,&b);
   printf("value after swap: %d %d",a,b);
   return 0;
}