プロジェクト2は複数クラスの演算子の再ロードを実現する(2)

/*copyright(c)2016.         
 * All rights reserved,
 *     ：text.Cpp
 *   ：   
 *     ：2016 5 12 
 *    ：vc++6.0
 *
 *     :        ，     
              ，           
                。
 */
#include<iostream>
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;
};
//        
Complex operator+(Complex &c1,Complex &c2)
{
    Complex c3;
    c3.real=c1.real+c2.real;
    c3.imag=c1.imag+c2.imag;
    return c3;

}
Complex operator-(Complex &c1,Complex &c2)
{
    Complex c3;
    c3.real=c1.real+c2.real;
    c3.imag=c1.imag+c2.imag;
    return c3;
}
Complex operator*(Complex &c1,Complex &c2)
{
    Complex c3;
    c3.real=c1.real*c2.real;
    c3.imag=c1.imag*c2.imag;
    return c3;
}
Complex operator/(Complex &c1,Complex &c2)
{
    Complex c3;
    c3.real=c1.real/c2.real;
    c3.imag=c1.imag/c2.imag;
    return c3;
}
void Complex::display()
{
    if(imag>0)
        cout<<real<<"+"<<imag<<"i"<<endl;
    else
        cout<<real<<imag<<"i"<<endl;
}
//         main()  
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;
}