[GCC] SWAP function --- Call by Address

#include "stdio.h"

void swap(int *x ,int *y);

void swap(int *x ,int *y)
{
  int tmp;
  tmp = *x;
  *x = *y;
  *y = tmp;
}

int main()
{
 int a = 1;
 int b = 2;

 printf("[before]  a=%d b=%d\r\n",a,b);
 swap(&a,&b);
 printf("[after]   a=%d b=%d\r\n",a,b);

return 0;
}

==============Result==============
(for Code::Block)

[before]  a=1 b=2
[after]     a=2 b=1