定义一个Point类，派生出Rectangle类和Circle类，计算各派生类对象的面积Area

#include <iostream>
using namespace std;

class Point {
protected:
    double x, y;
public:
    Point(double x = 0, double y = 0) {
        this->x = x;
        this->y = y;
    }
    virtual double Area() = 0;
};

class Rectangle : public Point {
private:
    double length, width;
public:
    Rectangle(double x = 0, double y = 0, double length = 0, double width = 0) : Point(x, y) {
        this->length = length;
        this->width = width;
    }
    double Area() {
        return length * width;
    }
};

class Circle : public Point {
private:
    double radius;
public:
    Circle(double x = 0, double y = 0, double radius = 0) : Point(x, y) {
        this->radius = radius;
    }
    double Area() {
        return 3.1415926 * radius * radius;
    }
};

int main() {
    Point* p;
    Rectangle r(0, 0, 3, 4);
    Circle c(0, 0, 5);
    p = &r;
    cout << "Rectangle Area: " << p->Area() << endl;
    p = &c;
    cout << "Circle Area: " << p->Area() << endl;
    return 0;
}