shiti3_5_2.cpp

为初学者提供的最佳的C++程序设计源程序库

 #include<iostream.h>
class Shape
{
public:
	Shape(double x){r=x;}
	virtual void area()=0;
	virtual void perimeter()=0;
protected:
	double r;
};
class Circle:public Shape
{
public:
	Circle(double x):Shape(x){}
	void perimeter(){cout<<"The circle's perimeter is "<<2*3.14*r<<endl;}
	void area(){cout<<"The circle's area is "<<r*3.14*r<<endl;}
};
class In_Square:public Shape
{
public:
	In_Square(double x):Shape(x){}
	void perimeter(){cout<<"The internal's perimeter is "<<4*1.41*r<<endl;}
	void area(){cout<<"The internal's area is "<<2*r*r<<endl;}
};
class Ex_Square:public Shape
{
public:
	Ex_Square(double x):Shape(x){}
	void perimeter(){cout<<"The external's perimeter is "<<8*r<<endl;}
	void area(){cout<<"The external's area is "<<4*r*r<<endl;}
};
void main()
{
	Shape *ptr;
	Circle obj1(5);
	In_Square obj2(5);
	Ex_Square obj3(5);
	ptr=&obj1;
	ptr->area();
	ptr->perimeter();
	ptr=&obj2;
	ptr->area();
	ptr->perimeter();
	ptr=&obj3;
	ptr->area();
	ptr->perimeter();
}