设计3个类：Shape，Circle和Rectangle，并根据main()函数能输出样例内容 Shape类中包括函数double calculateArea() {return 0.0;} Circle类继承自Shape类，包括新数据成员double radius， 继承的double calculateArea()返回3.14159 * radius * radius Rectangle类继承自Shape类，包括新数据成员double width和double height 继承的double calculateArea()返回cwidth * height 此外，要求： 1. 为类设计能够初始化数据成员的构造函数， 2. 数据成员访问控制优先使用private其次protected再次public 3. 给定函数返回值不能修改

下面是代码实现：

#include<iostream>
using namespace std;

class Shape {
public:
    virtual double calculateArea() const { return 0.0; }
};

class Circle : public Shape {
private:
    double radius;
public:
    Circle(double r) : radius(r) {}
    double calculateArea() const override {
        return 3.14159 * radius * radius;
    }
};

class Rectangle : public Shape {
private:
    double width, height;
public:
    Rectangle(double w, double h) : width(w), height(h) {}
    double calculateArea() const override {
        return width * height;
    }
};

int main() {
    Shape* shape1 = new Circle(2.5);
    Shape* shape2 = new Rectangle(3.0, 4.0);
    cout << "The area of the circle is: " << shape1->calculateArea() << endl;
    cout << "The area of the rectangle is: " << shape2->calculateArea() << endl;
    delete shape1;
    delete shape2;
    return 0;
}

输出结果：

The area of the circle is: 19.6349
The area of the rectangle is: 12