重载“-”运算符，使该运算符可以直接求出任意两点p1(X,Y)和p2(X,Y)之间的距离d，即d=p1-p2。

#include <iostream>
using namespace std;
class complex
{
public:
    complex ()
    {
        real=0;
        imag=0;
    }
    complex(double r,double i)
    {
        real=r;
        imag=i;
    }
    complex operator -(complex &c2);
    void display();
private:
    double real;
    double imag;
};
complex complex::operator -(complex &c2)
{
    return complex(real-c2.real,imag-c2.imag);
}
void complex::display()
{
    cout<<"("<<real<<","<<imag<<"i)"<<endl;
}
int main()
{
    complex c1(3,4),c2(5,-10),c3;
    c3=c1-c2;
    cout<<"c1=";
    c1.display();
    cout<<"c2=";
    c2.display();
    cout<<"c3=";
    c3.display();
    return 0;
}