《第十三周實驗報告任務3》

#include<iostream>   

using namespace std;  
  
const double PI = 3.14159;  
  
class Shape  
{  
public:  
    virtual double area() const =0;    //定義純虛函數，供派生類使用
};  
  
class Circle: public Shape  
{  
public:  
    Circle(double radius);                                    
    virtual double area() const;  
protected:  
    double radius;                                                 //半徑   
};  
  
class Rectangle: public Shape  
{  
public:  
    Rectangle(double length, double width);  
    virtual double area() const;  
protected:  
    double length;  
    double width;  
};  
  
class Triangle: public Shape  
{  
public:  
    Triangle(double base, double height);  
    virtual double area() const;  
protected:  
    double base;  
    double height;  
};  
  
Circle::Circle(double radius)  
{  
    this->radius = radius;  
}  
  
double Circle::area() const  
{  
    return PI * radius * radius;  
}  
  
Rectangle::Rectangle(double length, double width)  
{  
    this->length = length;  
    this->width = width;  
}  
  
double Rectangle::area() const  
{  
    return length * width;  
}  
  
Triangle::Triangle(double base, double height)  
{  
    this->base = base;  
    this->height = height;  
}  
  
double Triangle::area() const  
{  
    return 0.5 * base * height;  
}  
  
int main()  
{  
    Circle c1(12.6), c2(4.9);    //建立Circle類對象c1,c2,參數為圓半徑   
    Rectangle r1(4.5, 8.4), r2(5.0, 2.5);       //建立Rectangle類對象r1,r2,參數為矩形長、寬   
    Triangle t1(4.5, 8.4), t2(3.4, 2.8);    //建立Triangle類對象t1,t2，參數為三角形底邊長與高   
    Shape *pt[6] = {&c1, &c2, &r1, &r2, &t1, &t2}; //定義基類指針數組pt，各元素指向一個派生類對象   
  
    double areas = 0.0;      //areas為總面積   
  
    for(int i = 0; i < 6; i++)  
    {  
        areas = areas + pt[i]->area();  
    }  
  
    cout << "totol of all areas=" << areas << endl;   //輸出總面積   
  
    system("pause");  
    return 0;  
}  

           

總結：

1、使用虛函數提高了程式的可擴充性

2、使用基類指針來控制有關對象，不管對象在繼承層次的那一層，都可以用基類指針指向它。