立体类族共有的抽象类

//
//  main.cpp
//  project
//
//  Created by 徐伟 on 6/5/16.
//  Copyright © 2016 fizz_i. All rights reserved.
//
/*  设计一个抽象类CSolid，含有用于求表面积及体积的两个纯虚函数。设计派生类CCube、CBall、CCylinder，分别表示正方体、球体及圆柱体。在main()函数中，定义CSolid *p;（p是指向基类的指针，且这个基类是个抽象类）。要求利用这个p指针，能够求出正方体、球体及圆柱体对象的表面积及体积。*/
#include <iostream>

using namespace std;
class CSolid
{
public:
    virtual double area()const=0;
    virtual double volume()const=0;
};
class CCube:public CSolid
{
public:
    CCube(double a=0):a(a){}
    double area()const;
    double volume()const;
private:
    double a;
};
double CCube::area()const
{
    return a*a*6;
}
double CCube::volume()const
{
    return a*a*a;
}

class CBall:public CSolid
{
public:
    CBall(double r=0):r(r){}
    double area()const;
    double volume()const;
private:
    double r;
};
double CBall::area()const
{
    return 4*3.1415926*r*r;
}
double CBall::volume()const
{
    return 4*3.1415926*r*r*r/3;
}

class CCylinder:public CCube
{
public:
    CCylinder(double r=0,double h=0):r(r),h(h){}
    double area()const;
    double volume()const;
private:
    double r;
    double h;
};
double CCylinder::area()const
{
    return 2*3.1415926*r*h+3.1415926*r*r;
}
double CCylinder::volume()const
{
    return 3.1415926*r*r*h;
}
int main( )
{
    CSolid *p;
    double s,v;
    CCube x(30);
    cout<<"立方体边长为 30 "<<endl;
    p=&x;
    s=p->area( );
    v=p->volume( );
    cout<<"表面积："<<s<<endl;
    cout<<"体积："<<v<<endl;
    cout<<endl;
    CBall y(4.5);
    cout<<"球体半径为 4.5 "<<endl;
    p=&y;
    s=p->area( );
    v=p->volume( );
    cout<<"表面积："<<s<<endl;
    cout<<"体积："<<v<<endl;
    cout<<endl;
    CCylinder z(10,20);
    cout<<"圆柱体底面半径、高分别为 10, 20"<<endl;
    p=&z;
    s=p->area( );
    v=p->volume( );
    cout<<"表面积："<<s<<endl;
    cout<<"体积："<<v<<endl;
    cout<<endl;
    return 0;
}