C :

#include <stdio.h>
#include <math.h>
int main ()
{
 int a,b,c;
 scanf("%d%d",&a,&b);
 c=a;
 a=b;
 b=c;
 printf("%d %d",a,b);
 return 0;
}

C++ :

#include "stdio.h"
#define swap(a,b) tem=a;a=b;b=tem;
int main(int argc, char* argv[])
{
	int tem,a,b;
	while(~scanf("%d%d",&a,&b))
	{
	  swap(a,b);
	  printf("%d %d\n",a,b);
	}
	return 0;
}