c++定义一个抽象类Shape，有2个纯虚函数计算体积和表面积：calVolume()和calArea(),返回值为double型。由Shape类派生出3种几何图形：正方体类，球体类和圆柱体类，各自新增的数据成员均为double型。 对于calVolume()和calArea()，每一个定义两个普通的重载函数：返回值均为void，形参分别是抽象类的对象指针、抽象类的对象引用，在函数中通过指针或引用调用虚函数calArea()或者calVolume()，输出结果。 在main函数中，进行测试，必须包含重载函

数的调用。代码如下：

#include <iostream>
using namespace std;

class Shape {
public:
    virtual double calVolume() = 0;
    virtual double calArea() = 0;
    virtual ~Shape() {}
};

class Cube : public Shape {
public:
    Cube(double l) : length(l) {}
    double calVolume() { return length * length * length; }
    double calArea() { return 6 * length * length; }
private:
    double length;
};

class Sphere : public Shape {
public:
    Sphere(double r) : radius(r) {}
    double calVolume() { return 4.0 / 3.0 * 3.1415926 * radius * radius * radius; }
    double calArea() { return 4 * 3.1415926 * radius * radius; }
private:
    double radius;
};

class Cylinder : public Shape {
public:
    Cylinder(double r, double h) : radius(r), height(h) {}
    double calVolume() { return 3.1415926 * radius * radius * height; }
    double calArea() { return 2 * 3.1415926 * radius * height + 2 * 3.1415926 * radius * radius; }
private:
    double radius;
    double height;
};

void calVolume(Shape* s) {
    cout << "The volume of the shape is " << s->calVolume() << endl;
}

void calArea(Shape& s) {
    cout << "The area of the shape is " << s.calArea() << endl;
}

int main() {
    Cube c(2);
    Sphere sp(3);
    Cylinder cy(2, 5);

    calVolume(&c);
    calArea(c);

    calVolume(&sp);
    calArea(sp);

    calVolume(&cy);
    calArea(cy);

    return 0;
}