1.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() （不能使用构造函数进行初始化)

以下是定义Point类，派生出Rectangle类和Circle类，计算各派生类对象的面积Area()的示例代码：

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

class Point {
protected:
    double x, y;
public:
    Point(double x = 0, double y = 0) : x(x), y(y) {}
    double getX() const { return x; }
    double getY() const { return y; }
};

class Rectangle : public Point {
private:
    double width, height;
public:
    Rectangle(double x = 0, double y = 0, double width = 0, double height = 0) : Point(x, y), width(width), height(height) {}
    double getWidth() const { return width; }
    double getHeight() const { return height; }
    double Area() const { return width * height; }
};

class Circle : public Point {
private:
    double radius;
public:
    Circle(double x = 0, double y = 0, double radius = 0) : Point(x, y), radius(radius) {}
    double getRadius() const { return radius; }
    double Area() const { return M_PI * pow(radius, 2); }
};

int main() {
    Rectangle rect(0, 0, 5, 10);
    Circle circle(0, 0, 5);
    cout << "Rectangle area: " << rect.Area() << endl;
    cout << "Circle area: " << circle.Area() << endl;
    return 0;
}

在这个示例中，定义了一个基类Point，它代表一个二维坐标点。Rectangle和Circle都是从Point派生出来的类。Rectangle和Circle都有各自的Area()函数来计算它们的面积。Area()函数在Rectangle类中计算矩形面积，在Circle类中计算圆面积。在main()函数中创建了一个Rectangle对象和一个Circle对象，并分别调用它们的Area()函数来计算它们的面积。