#include <iostream>
#include <string>

using namespace std;

class Parent
{
protected:
    int mv;
public:
    Parent()
    {
        mv = 100;
    }
    
    int value()
    {
        return mv;
    }
};

class Child : public Parent
{
public:
    int addValue(int v)
    {
        mv = mv + v;    //可以访问父类的私有成员
    }
};

int main()
{   
    Parent p;
    
    cout << "p.mv = " << p.value() << endl;
    
    // p.mv = 1000;    // error， protected
    
    Child c;
    
    cout << "c.mv = " << c.value() << endl;//继承了父类的成员函数
    
    c.addValue(50);
    
    cout << "c.mv = " << c.value() << endl;
    
    // c.mv = 10000;  // error， protected
    
    return 0;
}

#include<iostream>
#include<string>
#include<sstream>

using namespace std;

class Object
{
protected:
    string mName;
    string mInfo;
public:
    Object()
    {
        mName = "Object";
        mInfo = "";
    }

    string name()
    {
        return mName;
    }

    string info()
    {
        return mInfo;
    }

};

class Point : public Object
{
private:
    int mX;
    int mY;
public:
    Point(int x=0, int y=0)
    {
        ostringstream s;
        mName = "Point";
        mX = x;
        mY = y;
        s << "p(" << mX << "," << mY << ")";
        mInfo = s.str();
    }
};

class Line : public Object
{
private:
    Point mP1;//Line 由 Point 组合而成
    Point mP2;
public:
    Line(Point P1, Point P2)
    {
        ostringstream s;
        
        mP1 = P1;
        mP2 = P2;
        mName = "Line";

        s << "Line from" << mP1.info() << "to" << mP2.info();
        mInfo = s.str();        
    }

    Point begin()
    {
        return mP1;
    }

    Point end()
    {
        return mP2;
    }
};

int main()
{
    Object o;
    Point p(1, 2);
    Point pn(5, 6);
    Line l(p, pn);

    cout << o.name() << endl;//Object
    cout << o.info() << endl;

    cout << endl;

    cout << p.name() << endl;//Point
    cout << p.info() << endl;//p(1, 2)

    cout << endl;

    cout << l.name() << endl;//Line
    cout << l.info() << endl;//Line fromP(1, 2)toP(5, 6)

    return 0;
}