C++ 虚函数实例

#include <iostream>
using namespace std;
//线
class Line
{
    public:
        Line(float len);
        virtual float area() = 0;
        virtual float volume() = 0;
    protected:
        float m_len;
};
Line::Line(float len): 
m_len(len) 
{ }

//矩形
class Rec: public Line
{
    public:
        Rec(float len, float width);
        float area();
    protected:
        float m_width;
};

Rec::Rec(float len, float width): 
Line(len), m_width(width) 
{ }

float Rec::area()
{
    return m_len * m_width;
}

//长方体
class Cuboid: public Rec
{
    public:
        Cuboid(float len, float width, float height);
        float area();
        float volume();
    protected:
        float m_height;
};
Cuboid::Cuboid(float len, float width, float height): 
Rec(len, width), m_height(height) 
{ }

float Cuboid::area()
{
    return 2 * ( m_len*m_width + m_len*m_height + m_width*m_height);
}
float Cuboid::volume()
{
    return m_len * m_width * m_height;
}

//正方体
class Cube: public Cuboid
{
    public:
        Cube(float len);
        float area();
        float volume();
};
Cube::Cube(float len): 
Cuboid(len, len, len)
{ }
 
float Cube::area()
{
    return 6 * m_len * m_len;
}
float Cube::volume()
{
    return m_len * m_len * m_len;
}


int main()
{
    Line *p = new Cuboid(10, 20, 30);
    cout<<"The area of Cuboid is " <<p->area()<<endl;
    cout<<"The volume of Cuboid is " <<p->volume()<<endl;

    p = new Cube(15);
    cout<<"The area of Cube is "<<p->area()<<endl;
    cout<<"The volume of Cube is "<<p->volume()<<endl;
    return 0;
}