[求助]引用问题

#include <iostream.h>
void fun(int *x,int y)
{
y=*x+y;
*x=y%4;
cout<<*x<<','<<y<<endl;
}
void main ()
{
int x=4; int y=5;
fun(&y,x);
cout<<x<<','<<y<<endl;
fun(&x,y);
cout<<x<<','<<y<<'\n';
}
帮忙解释下该程序呀