运算符重载

根据以下代码段完善 ?? 处内容及程序内容，以实现规定的输出。

class Complex
{
    public:
        Complex(double r=0, double i=0):real(r), imag(i){    }
        Complex operator+( ?? ) const;//重载双目运算符'+'
        Complex operator-=( ?? ); //重载双目运算符'-='
        friend Complex operator-( ?? ) const;//重载双目运算符'-'
        void Display() const;
    private:
        double real;
        double imag;
};

void Complex::Display() const
{
    cout << "(" << real << ", " << imag << ")" << endl;
}

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;
}

 

输入格式:

输入有两行，分别为两个复数的实部与虚部。

输出格式:

按样例格式输出结果。

输入样例:

在这里给出一组输入。例如：

4 2
3 -5

输出样例:

在这里给出相应的输出。例如：

(7, -3)
(1, 7)
(-3, 5)

#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&c2 ); //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;
};
Complex Complex::operator +(Complex &c2)const
{
    return Complex(real+c2.real,imag+c2.imag);
}
Complex Complex::operator -=(Complex&c2)
{
    return Complex(real-=c2.real,imag-=c2.imag);
}
Complex operator -(Complex &c1,Complex &c2)
{
    return Complex(c1.real-c2.real,c1.imag-c2.imag); 
 }
void Complex::Display() const
{
    cout << "(" << real << ", " << imag << ")" << endl;
}

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;
}