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;
}

　　

 1 #include<iostream>
 2 using namespace std;
 3 
 4 class Complex
 5 {
 6     public:
 7         Complex(double r=0,double i=0):real(r), imag(i){}
 8         Complex operator+(Complex &) const;//重载双目运算符'+'
 9         Complex operator-=(Complex &); //重载双目运算符'-='
10         friend  const Complex operator-(Complex &,Complex &);//重载双目运算符'-'
11         void Display() const;
12     private:
13         double real;
14         double imag;
15 };
16 
17 Complex Complex::operator + (Complex &C) const
18 {
19     return Complex(real+C.real,imag+C.imag);        //重载 + 返回值为相加之后的结果
20 }
21 
22 Complex Complex::operator-=(Complex &C)
23 {
24     real=real-C.real;
25     imag=imag-C.imag;
26     return Complex(real,imag);          //重载 -= 返回值为减后结果，且对象本身数值也发生变化
27 }
28 
29 Complex const operator - (Complex &C1,Complex &C2)  //重载 - 返回值为相减后的结果
30 {
31     return Complex(C1.real-C2.real,C1.imag-C2.imag);
32 }
33 
34 void Complex::Display() const
35 {
36     cout << "(" << real << ", " << imag << ")" << endl;
37 }
38 
39 int main()
40 {
41     double r, m;
42     cin >> r >> m;
43     Complex c1(r, m);
44     cin >> r >> m;
45     Complex c2(r, m);
46     Complex c3 = c1+c2;
47     c3.Display();
48     c3 = c1-c2;
49     c3.Display();
50     c3 -= c1;
51     c3.Display();
52     return 0;
53 }