7-4 复数类的运算 (20 分)

#include <iostream>
using namespace std;
class Complex
{
    public:
        Complex(double r=0, double i=0):real(r), imag(i){    }
        Complex operator+( Complex &c2) const;//重载双目运算符'+'
        Complex operator-=( Complex &c1 ); //重载双目运算符'-='
        friend Complex operator-( Complex &c1,Complex &c2) ;//重载双目运算符'-'
        void Display() const;
    private:
        double real;
        double imag;
};

void Complex::Display() const
{
    cout << "(" << real << ", " << imag << ")" << endl;
}
Complex Complex::operator+( Complex &c2) const
{
    return Complex(real+c2.real,imag+c2.imag);
}
Complex Complex::operator-=( Complex &c)
{
    this->imag=this->imag-c.imag;
    this->real=this->real-c.real;
    return *this;
}
 Complex operator-( Complex &c1,Complex &c2 )
 {
      return Complex(c1.real-c2.real,c1.imag-c2.imag);
 }
int main()
{
    double r, m;
    cin >> r >> m;
    Complex c1(r, m);
    cin >> r >> m;
    Complex c2(r, m);
    Complex c3 = c1+c2;
    c3.Display();
    c3 = c1-c2;
    c3.Display();
    c3 -= c1;
    c3.Display();
    return 0;
}