求助，照着书里的代码打的，但是总报语法错误

#include "stdio.h"
#include "conio.h"
#define exchange(a,b)
{\
int t;\
t=a;\
a=b;\
b=t;\
}
void main(void)
{
int x=10;
int y=20;
printf("x=%d;y=%d\n",x,y);
exchange(x,y);
printf("x=%d;y=%d\n",x,y);
getch();
}