编写一个程序，声明抽象基类Shape，由它派生出3个派生类：Circle（圆形）、Rectangle（矩形）、Triangle（三角形），用一个函数printArea分别输出以上三者的面积，3个图形的

编写一个程序，声明抽象基类Shape，由它派生出3个派生类：Circle（圆形）、Rectangle（矩形）、Triangle（三角形），用一个函数printArea分别输出以上三者的面积，3个图形的数据在定义对象时给定。

#include
using namespace std;

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



class Circle:public Shape
{
	public:
		Circle(double r):radius(r)
		{
			
		}
		virtual double area() const
		{
			return 3.14159*radius*radius;
		}
	protected:
		double radius;
};



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



class Triangle:public Shape
{
	public:
		Triangle(double w,double h):width(w),height(h)
		{
			
		}
		virtual double area() const
		{
			return 0.5*width*height;
		}
	protected:
		double width,height;
};


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





int main()
{
	Circle circle(12.6);
	cout<<"area of circle = ";
	printArea(circle);
	
	Rectangle rectangle(4.5,8.4);
	cout<<"area of rectangle = ";
	printArea(rectangle);
	
	Triangle triangle(4.5,8.4);
	cout<<"area of triangle = ";
	printArea(triangle);
	
	return 0;
}