习题4

定义抽象基类Shape

#include <iostream>
using namespace std;

class Shape
{
public:
     virtual float area() const =0;
};

class Circle:public Shape
{
public:
     Circle(float r):radius(r){}
     virtual float area() const
     {
         return 3.14 * radius * radius;
     }

 protected:
     float radius;
 };

派生类Circle(圆形)

class Circle:public Shape
{
public:
     Circle(float r):radius(r){}
     virtual float area() const
     {
         return 3.14 * radius * radius;
     }

protected:
     float radius;
};

派生类Rectangle(矩形)

class Rectangle: public Shape
{
public:
     Rectangle(float h, float w): height(h), width(w){}
     virtual float area() const
     {
         return height * width;
     }

 protected:
     float height;
     float width;
 };

派生类Triangle（三角形）

class Triangle: public Shape
{
public:
     Triangle(float h, float l): height(h), lenght(l){}
     virtual float area() const
     {
         return 0.5 * height * lenght;
     }

protected:
     float height;
     float lenght;
};

输出面积的函数printArea

void printArea(const Shape &s)
{
 cout << s.area()<<endl;
}

写main函数

int main()
{
    Circle circle(2.4);
    cout << "圆的面积是: ";
    printArea(circle);

    Rectangle rectangle(1.3, 1.4);
    cout <<"矩形的面积是： ";
    printArea(rectangle);

    Triangle tri(2.4, 5.9);
    cout << "三角形的面积是：";
    printArea(tri);

    return 0;

}

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