帮忙看看哪出问题了

#include<iostream.h>
class   fushu
{
protected: int sb,xb;
public: fushu(int x,int y){sb=x;xb=y;}
        friend fushu operator * (fushu f1,fushu f2);
        void display()
        {cout<<sb<<"+"<<xb<<"i"<<endl;}
   
   
};


fushu operator * (fushu f1,fushu f2)
{
       fushu f;
        f.sb=f1.sb*f2.sb-f1.xb*f2.xb;
        f.xb=f1.sb*f2.xb+f1.xb*f2.sb;
        return fushu(f.sb,f.xb);}
void main(void){
fushu a(2,3),b(4,5),c(0,0),d(0,0);
c=a*b;
c.display();
}