友元成员简单应用

/****************************************************
* 文件名：
* 功能：友元成员简单应用
* 说明：友元提供了不同类的成员函数之间、
        类的成员函数与一般函数之间进行数据共享的机制
* 时间：2011-3-30 --Lzy
****************************************************/

//普通函数作为友元函数

#include <iostream.h>
#include <math.h>

const double PI = 3.141593;        //定义常量


class Circle
{
private:
    double x, y,r;

public:
    Circle(double xx = 0, double yy = 0, double rr = 0)
    {
        x = xx; y = yy; r = rr;
    }

    void display()
    {
        cout<<"中点"<<"("<<x<<" ,"<<y<<")"<<endl;
        cout<<"半径"<<r<<endl;
        cout<<"面积"<<this->area()<<endl;
        cout<<"周长"<<this->circular()<<endl;
    }

    double area(){return PI*r*r;}
    double circular(){return 2*PI*r;}
    friend double distance(Circle &p1, Circle &p2);            //普通函数作友元函数

};

double distance(Circle &p1, Circle &p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}

void main(void)
{
    Circle c1(1,1,1), c2(3,3,3);
    c1.display();
    c2.display();
    cout<<distance(c1,c2);
}


//成员函数作为友元函数

#include <iostream.h>
#include <math.h>

const double PI = 3.141593;        //定义常量


class Circle;            //前向声明


class Calculate
{
public:
    double distance(Circle &p1, Circle &p2);
};

class Circle
{
private:
    double x, y,r;

public:
    Circle(double xx = 0, double yy = 0, double rr = 0)
    {
        x = xx; y = yy; r = rr;
    }

    void display()
    {
        cout<<"中点"<<"("<<x<<" ,"<<y<<")"<<endl;
        cout<<"半径"<<r<<endl;
        cout<<"面积"<<this->area()<<endl;
        cout<<"周长"<<this->circular()<<endl;
    }

    double area(){return PI*r*r;}
    double circular(){return 2*PI*r;}
    friend double Calculate::distance(Circle &p1, Circle &p2);            //友元函数

};

double Calculate::distance(Circle &p1, Circle &p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}

void main(void)
{
    Circle c1(1,1,1), c2(3,3,3);
    Calculate cal;
    c1.display();
    c2.display();
    cout<<cal.distance(c1,c2)<<endl;
}

//友元类

#include <iostream.h>
#include <math.h>

const double PI = 3.141593;        //定义常量


class Circle;            //前向声明


class Calculate
{
public:
    double distance(Circle &p1, Circle &p2);
    double area(Circle &c);
    double circular(Circle &c);
    void display(Circle &c);
};

class Circle
{

public:
    double x, y,r;
    Circle(double xx = 0, double yy = 0, double rr = 0)
    {
        x = xx; y = yy; r = rr;
    }

    void display()
    {
        cout<<"中点"<<"("<<x<<" ,"<<y<<")"<<endl;
        cout<<"半径"<<r<<endl;
    }

    friend class Calulate;

};

double Calculate::distance(Circle &p1, Circle &p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}

double Calculate::area(Circle &c)
{
    return PI*c.r*c.r;
}

double Calculate::circular(Circle &c)
{
    return PI*c.r*2;
}

void Calculate::display(Circle &c)
{
    cout<<"面积"<<this->area(c)<<endl;
    cout<<"周长"<<this->circular(c)<<endl;
}

void main(void)
{
    Circle c1(1,1,1), c2(3,3,3);
    Calculate cal;
    c1.display();
    c2.display();
    cout<<cal.distance(c1,c2)<<endl;
}