运算符重载--友元

/*
*Corpyright (c)2013,烟台大学计算机学院
*All right reseved.
*作者：马广明
*完成日期：2014年4月15日
*版本号：v1.0
*问题描述:运算符重载
*/
#include <iostream>
#include <cmath>
using namespace std;
class Complex
{
public:
    Complex(){real=0;imag=0;}
    Complex(double r,double i){real=r; imag=i;}
    friend Complex operator+(Complex &c1,Complex &c2);
    friend Complex operator-(Complex &c1,Complex &c2);
    friend Complex operator*(Complex &c1,Complex &c2);
    friend Complex operator/(Complex &c1,Complex &c2);
    void display();
private:
    double real;
    double imag;
};
void Complex::display()
{
    cout<<"("<<real<<","<<imag<<")"<<endl;
}
Complex operator+(Complex &c1,Complex &c2)
{
    Complex c;
    c.real=c1.real+c2.real;
    c.imag=c1.imag+c2.imag;
    return c;
}
Complex operator-(Complex &c1,Complex &c2)
{
    Complex c;
    c.real=c1.real-c2.real;
    c.imag=c1.imag-c2.imag;
    return c;
}
Complex operator*(Complex &c1,Complex &c2)
{
    Complex c;
    c.real=c1.real*c2.real-c1.imag+c2.imag;
    c.imag=c1.imag*c2.real+c1.real*c2.imag;
    return c;
}
Complex operator/(Complex &c1,Complex &c2)
{
    Complex c;
    c.real=(c1.real*c2.real+c1.imag+c2.imag)/(c2.real*c2.real+c2.imag*c2.imag);
    c.imag=(c1.imag*c2.real-c1.real*c2.imag)/(c2.real*c2.real+c2.imag*c2.imag);
    return c;
}
int main()
{
    Complex c1(3,4),c2(5,-10),c3;
    cout<<"c1=";
    c1.display();
    cout<<"c2=";
    c2.display();
    c3=c1+c2;
    cout<<"c1+c2=";
    c3.display();
    c3=c1-c2;
    cout<<"c1-c2=";
    c3.display();
    c3=c1*c2;
    cout<<"c1*c2=";
    c3.display();
    c3=c1/c2;
    cout<<"c1/c2=";
    c3.display();
    return 0;
}