#include<stdio.h>
#include<math.h>

#define exchange(a,b){\
                        int t;\   
                        t=a;\
                        a=b;\
                        b=t;\
                        }


void main()
{
    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);
}
这里宏定义怎么理解？