C++面向對象友元函數運算符的重載

以課本複數類爲例：

具體看代碼，哪裏不懂可以評論留言。

#include <iostream>
using namespace std;
class Complex{
	public:
		Complex(){real = 0,imag = 0;}
		Complex(double r=0,double i=0):real(r),imag(i){}
		void display();
		friend Complex operator+(Complex,Complex);
		Complex operator++();
		Complex operator++(int);
	//	operator double(){return real;}
		friend ostream& operator <<(ostream&,Complex&);
		friend istream& operator >>(istream&,Complex&);
	private:
		double real,imag;
}; 
void Complex::display(){
	cout<<"("<<real<<","<<imag<<"i)"<<endl;
}
Complex operator+(Complex c1,Complex c2){
	return Complex(c1.real+c2.real,c1.imag+c2.imag);
}
Complex Complex::operator++(){
	real++;
	imag++;
	return *this;
}
Complex Complex::operator++(int){
	real++;
	imag++;
	return *this;
}
ostream & operator <<(ostream &x,Complex &c){
	x<<"("<<c.real<<","<<c.imag<<"i)";
	return x;
}
istream & operator >>(istream&x,Complex &c){
	x>>c.real>>c.imag;
	return x;
}
int main(){
	
	Complex c1(9,5),c2(1,1);
//	cin>>c1>>c2;
	c1.display();	
	c2.display();
	(c1+c2).display();
	++c2;
	c2.display();
	c1++;
	(c1+c2).display();
	Complex c = c1+c2;
	cout<<c;
	double d;
	c = 2.5 + c1;
	cout<<c<<endl;
	c = c1+1.5;
	cout<<c<<endl;
	return 0;
}