2.先建立一个Point（点）类，包含数据成员x,y（坐标点）。以它为基类，派生出一个Circle（圆）类，增加数据成员r（半径），再以Circle类为直接基类，派生出一个Cylinder（圆柱体）类，在增加数据成员h（高）。要求编写程序，重载运算符“<<”和“>>”，求解圆的面积和圆柱体

的体积，同时能够输入和输出圆和圆柱体对象的信息。

以下是基于您的要求编写的代码：

#include <iostream>
using namespace std;

const double PI = 3.14159265358979323846;

class Point {
public:
    Point(double xx = 0, double yy = 0) : x(xx), y(yy) {}
    friend istream& operator>>(istream& is, Point& p);
    friend ostream& operator<<(ostream& os, const Point& p);
protected:
    double x, y;
};

istream& operator>>(istream& is, Point& p) {
    is >> p.x >> p.y;
    return is;
}

ostream& operator<<(ostream& os, const Point& p) {
    os << "(" << p.x << ", " << p.y << ")";
    return os;
}

class Circle : public Point {
public:
    Circle(double xx = 0, double yy = 0, double rr = 0) : Point(xx, yy), r(rr) {}
    double area() const { return PI * r * r; }
    friend istream& operator>>(istream& is, Circle& c);
    friend ostream& operator<<(ostream& os, const Circle& c);
protected:
    double r;
};

istream& operator>>(istream& is, Circle& c) {
    is >> static_cast<Point&>(c) >> c.r;
    return is;
}

ostream& operator<<(ostream& os, const Circle& c) {
    os << "Center: " << static_cast<const Point&>(c) << ", Radius: " << c.r;
    return os;
}

class Cylinder : public Circle {
public:
    Cylinder(double xx = 0, double yy = 0, double rr = 0, double hh = 0) : Circle(xx, yy, rr), h(hh) {}
    double volume() const { return Circle::area() * h; }
    friend istream& operator>>(istream& is, Cylinder& cy);
    friend ostream& operator<<(ostream& os, const Cylinder& cy);
protected:
    double h;
};

istream& operator>>(istream& is, Cylinder& cy) {
    is >> static_cast<Circle&>(cy) >> cy.h;
    return is;
}

ostream& operator<<(ostream& os, const Cylinder& cy) {
    os << "Base: " << static_cast<const Circle&>(cy) << ", Height: " << cy.h;
    return os;
}

int main() {
    Circle c(0, 0, 1);
    cout << "Input circle info: ";
    cin >> c;
    cout << c << endl;
    cout << "Circle area: " << c.area() << endl;

    Cylinder cy(0, 0, 1, 2);
    cout << "Input cylinder info: ";
    cin >> cy;
    cout << cy << endl;
    cout << "Cylinder volume: " << cy.volume() << endl;

    return 0;
}

在上面的代码中，Point类表示一个点，包含x和y坐标；Circle类继承自Point类，并增加了一个r成员表示半径，同时提供了计算面积的方法area()；Cylinder类继承自Circle类，并增加了一个h成员表示高，同时提供了计算体积的方法volume()。重载运算符“<<”和“>>”用于输入和输出对象信息。在main函数中，先创建一个Circle对象和一个Cylinder对象，然后输入它们的信息并计算面积和体积，最后输出结果。