C++继承与多态练习--计算图形面积

/*//修改--5-16-关于球体表面积和体积公式错误*/

/*设计一个计算图形面积的类库。
类库的顶层是一个抽象类，并且提供三个纯虚函数；显示数据成员、返回面积和返回体积。
Class Shape
{
virtual void showData()=0;
virtual double reArea()=0;
virtual double reVolume()=0;
};
第二层由Shape类派生TwoDimShape（二维图形）和ThreeShape（三维图形），
它们增加了有关的数据成员，但没有成员函数的实现。
第三层派生具体的图形类。TwoDimShape类派生Circle（圆）、Elipse（椭圆）、
Rectangle（矩形）和Triangle（三角形）等类。
ThreeShape类派生Ball（球体）、Cylinder（圆柱体）、
RectangularParallelepiped（长方体）等类。
在主函数测试中使用多态方式调用不同对象的求值函数。
*/

/*
*This file contains code for C++ 6th experiment
*By LZH
*/
#include<iostream>
#include<string>
using namespace std;
const double PI = acos(-1.0);
// Definition of Shape class and related functions goes here
class Shape
{
    virtual void showData() = 0;
    virtual double reArea() = 0;
    virtual double reVolume() = 0;
};
class TwoDimShape :virtual public Shape {
protected:
    double x, y;
public:
    virtual void showData() {
        return ;
    }
    virtual double reArea() {
        return 0;
    }
    virtual double reVolume() {
        return 0;
    }
};
class ThreeShape :virtual public Shape {
protected:
    double x, y, z;
public:
    virtual void showData() {
        return;
    }
    virtual double reArea() {
        return 0;
    }
    virtual double reVolume() {
        return 0;
    }
};
class Circle :virtual public TwoDimShape {
public:
    Circle(double tp) {
        x = tp;
    }
    Circle(Circle &asp) {
        x = asp.x;
    }
    ~Circle()
    {

    }
    void showData() {
        cout << "This is a Circle:" << endl
            << "The radiation:" << x << endl
            << "The area:" << reArea() << endl;
    }
    double reArea() {
        return PI*x*x;
    }
};
class Elipse :virtual public TwoDimShape {
public:
    Elipse(double ta, double tb) {
        x = ta, y = tb;
    }
    Elipse(Elipse &asp) {
        x = asp.x, y = asp.y;
    }
    ~Elipse() {

    }
    void showData() {
        cout << "This is a Elipse:" << endl
            << "The long axis:" << x << endl
            << "The short axis:" << y << endl
            << "The area:" << reArea() << endl;
    }
    double reArea() {
        return PI*x*y;
    }
};
class Rectangle :virtual public TwoDimShape {
public:
    Rectangle(double ta, double tb) {
        x = ta, y = tb;
    }
    Rectangle(Rectangle &asp) {
        x = asp.x, y = asp.y;
    }
    ~Rectangle() {

    }
    void showData() {
        cout << "This is a Rectangle:" << endl
            << "The long axis:" << x << endl
            << "The short axis:" << y << endl
            << "The area:" << reArea() << endl;
    }
    double reArea() {
        return x*y;
    }
};
class Triangle :virtual public TwoDimShape {
public:
    Triangle(double ta, double tb) {
        x = ta, y = tb;
    }
    Triangle(Triangle &asp) {
        x = asp.x, y = asp.y;
    }
    ~Triangle() {

    }
    void showData() {
        cout << "This is a Triangle:" << endl
            << "The base length:" << x << endl
            << "The height  :" << y << endl
            << "The area:" << reArea() << endl;
    }
    double reArea() {
        return x*y / 2.0;
    }
};
class Ball :virtual public ThreeShape {
public:
    Ball(double ta) {
        x = ta;
    }
    Ball(Ball &asp) {
        x = asp.x;
    }
    ~Ball() {

    }
    void showData() {
        cout << "This is a Ball:" << endl
            << "The radiation:" << x << endl
            << "The surface area:" << reArea() << endl;
    }
    double reVolume() {
        return PI*pow(x, 3)*4.0 / 3.0;
    }
    double reArea() {
        return PI*x*x;
    }
};
class Cylinder :virtual public ThreeShape {
public:
    /*
    V=PI*r*r*h S=2*PI*r+r*h
    */
    Cylinder(double ta, double tb) {
        x = ta, y = tb;
    }
    Cylinder(Cylinder &asp) {
        x = asp.x, y = asp.y;
    }
    ~Cylinder() {

    }
    void showData() {
        cout << "This is a Cylinder:" << endl
            << "The radiation:" << x << endl
            << "The height:" << y << endl
            << "The surface area:" << reArea() << endl;
    }
    double reArea() {
        return 2 * PI*x + x*y;
    }
    double reVolume() {
        return PI*x*x*y;
    }
};
//RectangularParallelepiped
class cuboid :virtual public ThreeShape {
public:
    cuboid(double ta, double tb, double tc) {
        x = ta, y = tb, z = tc;
    }
    cuboid(cuboid &asp) {
        x = asp.x, y = asp.y, z = asp.z;
    }
    void showData() {
        cout << "This is a cuboid:" << endl
            << "The length:" << x << endl
            << "The width:" << y << endl
            << "The height" << z << endl
            << "The surface area:" << reArea() << endl;

    }
    double reArea() {
        return 2 * (x*y + x*z + y*z);
    }
    double reVolume() {
        return x*y*z;
    }
};
int main(void) {
    TwoDimShape a;
    ThreeShape b;
    TwoDimShape *p = &a;
    ThreeShape *w = &b;
    Circle t1(1.0);
    Elipse t2(1.0, 2.0);
    Rectangle t3(10.0,2.3);
    Triangle t4(4.0, 5.0);
    Ball t5(2.33333);
    Cylinder t6(4.5, 65.0);
    cuboid t7(132, 5,156);
    p = &t1;
    p->showData();
    p = &t2;
    p->showData();
    p = &t3;
    p->showData();
    p = &t4;
    p->showData();
    w = &t5;
    w->showData();
    w = &t6;
    w->showData();
    w = &t7;
    w->showData();
    return 0;
}

 在这个例子中我用了基类指针指向基类，这个不难理解，在类型兼容规则下，
 指向基类的指针可以隐式的转换成派生类的指针。
 这是最常见的关于多态的用法，利用该指针指向任意一个子类对象，
 就可以调用相应的虚函数，指向的子类的不同，实现的方法也就不同。