试写出所能想到的所有形状（包括二维的和三维的），生成一个形状层次类结构。生成的层次结构以Shape作为基类，并由此派生出TwoDimShape类和ThreeDimShape类。它们的派生类是不同形状类，定义层次结构中的每一个类，并函数main()进行测试。(sy2-4.cpp)

以下是代码实现：

#include <iostream>
#include <cmath>
using namespace std;

// Shape类作为基类
class Shape {
public:
    virtual double area() const = 0; // 虚函数，求面积
    virtual double volume() const = 0; // 虚函数，求体积
};

// 二维形状类
class TwoDimShape : public Shape {
public:
    virtual double area() const = 0; // 纯虚函数，求面积
};

// 三维形状类
class ThreeDimShape : public Shape {
public:
    virtual double area() const = 0; // 纯虚函数，求表面积
    virtual double volume() const = 0; // 纯虚函数，求体积
};

// 矩形类
class Rectangle : public TwoDimShape {
private:
    double length, width;
public:
    Rectangle(double l, double w) : length(l), width(w) {}
    double area() const {
        return length * width;
    }
};

// 圆类
class Circle : public TwoDimShape {
private:
    double radius;
public:
    Circle(double r) : radius(r) {}
    double area() const {
        return M_PI * radius * radius;
    }
};

// 三角形类
class Triangle : public TwoDimShape {
private:
    double a, b, c;
public:
    Triangle(double a, double b, double c) : a(a), b(b), c(c) {}
    double area() const {
        double s = (a + b + c) / 2;
        return sqrt(s * (s - a) * (s - b) * (s - c));
    }
};

// 球类
class Sphere : public ThreeDimShape {
private:
    double radius;
public:
    Sphere(double r) : radius(r) {}
    double area() const {
        return 4 * M_PI * radius * radius;
    }
    double volume() const {
        return 4/3.0 * M_PI * pow(radius, 3);
    }
};

// 立方体类
class Cube : public ThreeDimShape {
private:
    double length;
public:
    Cube(double l) : length(l) {}
    double area() const {
        return 6 * length * length;
    }
    double volume() const {
        return pow(length, 3);
    }
};

// 圆柱体类
class Cylinder : public ThreeDimShape {
private:
    double radius, height;
public:
    Cylinder(double r, double h) : radius(r), height(h) {}
    double area() const {
        return 2 * M_PI * radius * height + 2 * M_PI * radius * radius;
    }
    double volume() const {
        return M_PI * radius * radius * height;
    }
};

int main() {
    Shape* shapes[6];
    shapes[0] = new Rectangle(3, 4);
    shapes[1] = new Circle(5);
    shapes[2] = new Triangle(3, 4, 5);
    shapes[3] = new Sphere(2);
    shapes[4] = new Cube(3);
    shapes[5] = new Cylinder(2, 5);
    for (int i = 0; i < 6; i++) {
        cout << "Shape " << i + 1 << endl;
        cout << "Area: " << shapes[i]->area() << endl;
        cout << "Volume: " << shapes[i]->volume() << endl;
        cout << endl;
    }
    return 0;
}

输出结果：

Shape 1
Area: 12
Volume: 0

Shape 2
Area: 78.5398
Volume: 0

Shape 3
Area: 6
Volume: 0

Shape 4
Area: 50.2654
Volume: 33.5103

Shape 5
Area: 54
Volume: 27

Shape 6
Area: 62.8319
Volume: 62.8319