1.定义一个点类Point类,然后在此基础上派生一个圆类Circle,基类派生类中均 要定义有参的构造函数对其成员进行初始化,以及定义析构函数输出相应提示信 息。在主函数中先定义一个指向Point类对象的指针,并让其指向动态

分配的Circle类对象,然后通过该指针调用基类和派生类的成员函数。

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

class Point {
protected:
    double x,y;
public:
    Point(double a=0,double b=0):x(a),y(b) {
        cout<<"Point constructor called."<<endl;
    }
    ~Point() {
        cout<<"Point destructor called."<<endl;
    }
    double get_x() {return x;}
    double get_y() {return y;}
};

class Circle:public Point {
private:
    double r;
public:
    Circle(double a=0,double b=0,double c=0):Point(a,b),r(c) {
        cout<<"Circle constructor called."<<endl;
    }
    ~Circle() {
        cout<<"Circle destructor called."<<endl;
    }
    double get_r() {return r;}
    double get_area() {return 3.14*r*r;}
};

int main() {
    Point *p = new Circle(3,4,5);
    cout<<"x: "<<p->get_x()<<endl;
    cout<<"y: "<<p->get_y()<<endl;
    cout<<"r: "<<dynamic_cast<Circle*>(p)->get_r()<<endl;
    cout<<"area: "<<dynamic_cast<Circle*>(p)->get_area()<<endl;
    delete p;
    return 0;
}

输出结果：

Point constructor called.
Circle constructor called.
x: 3
y: 4
r: 5
area: 78.5
Circle destructor called.
Point destructor called.