C++面向对象程序设计实验题

Question

定义一个抽象类，并派生出矩形类和圆形类，二者都有函数计算对象的面积，并写出main（）函数进行测试。设矩形对象的长为了8，宽为5；圆形对象的半径为2.8。

Answer 1

#include<iostream>
using namespace std;
#define PI 3.14159
class shape{
public:
    virtual float getPerim() const =0;
    virtual void getName()const{cout<<"shape：";}
    shape(){}
    ~shape(){}
};

class Rectangle:public shape{
public:
    Rectangle(){}
    ~Rectangle(){}
    Rectangle(float l,float w):length(l),width(w){}
    virtual float getPerim() const;
    virtual void getName()const{cout<<"Rectangle:";}
private:
    float length,width;
};
float Rectangle::getPerim() const{
    return length*width;
}

class Circle :public shape{
public:
    Circle(){}
    Circle(float r):radius(r){}
    ~Circle(){}
    virtual float getPerim()const;
    virtual void getName()const{cout<<"Circle:";}
private:
    float radius;

};
float Circle::getPerim()const{
    return PI*radius*radius;
}

int main(){
    shape *sp;
    Circle circle(2.8);
    Rectangle rectangle(8,5);
    /*普通的访问方式，另一种是使用指针实现动态多态
    circle.getName();
    cout<<circle.getPerim()<<endl;
    rectangle.getName();
    cout<<rectangle.getPerim()<<endl;
    */
    sp=&circle;
    sp->getName();
    cout<<sp->getPerim()<<endl;
    sp=&rectangle;
    sp->getName();
    cout<<sp->getPerim()<<endl;

}