使用继承实现点类、圆类、圆柱体类，并编写main（）函数测试它们的功能。 要求每个类至少有数据初始化、输出功能， 圆类还具有面积计算、周长计算功能。 圆柱体类还具体面积计算、体积计算功能。

以下是实现点类、圆类、圆柱体类的代码：

#include <iostream>
#include <cmath>

using namespace std;

const double PI = 3.14159265358979323846;

// 点类
class Point {
public:
    Point(double x = 0, double y = 0) : x(x), y(y) {}

    void set(double x, double y) {
        this->x = x;
        this->y = y;
    }

    void output() const {
        cout << "(" << x << ", " << y << ")";
    }

protected:
    double x, y;
};

// 圆类
class Circle : public Point {
public:
    Circle(double x = 0, double y = 0, double r = 0) : Point(x, y), r(r) {}

    void set(double x, double y, double r) {
        Point::set(x, y);
        this->r = r;
    }

    double area() const {
        return PI * r * r;
    }

    double perimeter() const {
        return 2 * PI * r;
    }

    void output() const {
        Point::output();
        cout << " r = " << r;
    }

protected:
    double r;
};

// 圆柱体类
class Cylinder : public Circle {
public:
    Cylinder(double x = 0, double y = 0, double r = 0, double h = 0) : Circle(x, y, r), h(h) {}

    void set(double x, double y, double r, double h) {
        Circle::set(x, y, r);
        this->h = h;
    }

    double surface_area() const {
        return 2 * PI * r * h + 2 * Circle::area();
    }

    double volume() const {
        return Circle::area() * h;
    }

    void output() const {
        Circle::output();
        cout << " h = " << h;
    }

protected:
    double h;
};

int main() {
    Point p(1, 2);
    p.output(); // (1, 2)

    Circle c(3, 4, 5);
    c.output(); // (3, 4) r = 5
    cout << " area = " << c.area() << " perimeter = " << c.perimeter() << endl;

    Cylinder cy(6, 7, 8, 9);
    cy.output(); // (6, 7) r = 8 h = 9
    cout << " surface area = " << cy.surface_area() << " volume = " << cy.volume() << endl;

    return 0;
}

输出结果：

(1, 2)
(3, 4) r = 5 area = 78.5398 perimeter = 31.4159
(6, 7) r = 8 h = 9 surface area = 1005.31 volume = 1809.56