复数类的运算

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)
代码：

#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;
};

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 &c2)
{ real-=c2.real;
imag-=c2.imag;

return Complex(real,imag);
}
Complex operator-( Complex c1, Complex c2)
{ c1.real=c1.real-c2.real;
c1.imag=c1.imag-c2.imag;
//return c1;
return c1;
}
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;
}