类构造函数

class complex
{
private:
    double re, im;
public:
    complex(double r = 0, double i = 0) : re(r), im(i) {}
};

传递参数

(double r) //值
(const complex &) //不改变
(ostream& os) // reference

Friend 友元

private:
		double re, im;
	friend compelx& _doap1(complex&, const )