寫一個程序，定義抽象基類Shape,由它派生出3個派生類

寫一個程序，定義抽象基類Shape,由它派生出3個派生類，Cirle（圓形、Rectangle（矩形）、Triangle（三角形）。用一個函數printArea 分別輸出以上三者的面積，3個圖形的數據在定義對象時給定、

 

#include<iostream>
using namespace std;
/*
    圓面積S=3.14*r*r
    矩形面積S=長*寬
    三角形面積S=(底*高)/2
*/
class Shape
{
public:
    virtual float area()const=0;

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

private:
    double r;
};

class Rectangle:public Shape
{
public:
    Rectangle(double a,double b):l(a),w(b){}
    virtual float area()const{return l*w;}

private:
    double l;
    double w;
};
class Triangle:public Shape
{
public:
    Triangle(double a,double b):d(a),h(b){}
    virtual float area()const{return (d*h)/2;}

private:
    double d;
    double h;
};
void printArea(const Shape &s1)
{
    cout<<s1.area()<<endl;
}
int main()
{

    Circle c1(6.5);
    cout<<"圓面積=";
    printArea(c1);
    Rectangle r1(3,6);
    cout<<"矩形面積=";
    printArea(r1);
    Triangle t1(4,2);
    cout<<"三角形面積=";
     printArea(t1);


}