#include<iostream.h>
class Complex
{public:
Complex(){real=0;imag=0;}
Complex(double r){real=r;imag=0;}
Complex(double r,double i){real=r;imag=i;}
friend Complex operator+(Complex &c1,Complex  &c2);
void display();
private:
    double real;
    double imag;
};
Complex operator+(Complex &c1,Complex &c2)
{return Complex(c1.real+c2.real,c1.imag+c2.imag);}
void Complex::display()
{cout<<"("<<real<<","<<imag<<"i)"<<endl;}
int main()
{Complex c1(3,4),c2(5,10),c3;
c3=c1+c2;
c3.display();
return 0;
}
这个程序不能运行。。但是把friend Complex operator+(Complex &c1,Complex  &c2);这一行改成friend Complex operator+(Complex c1,Complex  c2);就没问题了。。请问为什么不能引用&???