#include <iostream>
#include <iomanip>
#include <cmath>

// 基类 Shape
class Shape {
public:
    // 虚函数 GetArea，用于计算面积
    virtual double GetArea() const = 0;
    // 虚析构函数
    virtual ~Shape() {}
};

// 派生类 Rectangle
class Rectangle : public Shape {
protected:
    double length;
    double width;

public:
    Rectangle(double l, double w) : length(l), width(w) {}
    // 实现 GetArea 函数
    double GetArea() const override {
        return length * width;
    }
};

// 派生类 Circle
class Circle : public Shape {
private:
    double radius;

public:
    Circle(double r) : radius(r) {}
    // 实现 GetArea 函数
    double GetArea() const override {
        return M_PI * radius * radius;
    }
};

// 派生类 Square，继承自 Rectangle
class Square : public Rectangle {
public:
    Square(double side) : Rectangle(side, side) {}
};

int main() {
    // 动态生成半径为5的圆对象
    Shape* circle = new Circle(5);
    std::cout << std::fixed << std::setprecision(1);
    std::cout << "The area of the Cirele is:" << circle->GetArea() << std::endl;

    // 恢复默认格式
    std::cout.unsetf(std::ios::fixed);
    std::cout.precision(6);

    // 动态生成长为4，宽为6的矩形对象
    Shape* rectangle = new Rectangle(4, 6);
    std::cout << "The area of the Recanale is:" << rectangle->GetArea() << std::endl;

    // 动态生成边为5的正方形对象
    Shape* square = new Square(5);
    std::cout << "The area of the Recanale is:" << square->GetArea() << std::endl;

    // 释放动态分配的内存
    delete circle;
    delete rectangle;
    delete square;

    return 0;
}