Exercise about Shape

 #include <iostream>
 using namespace std;
 class point
 {
     int x;
     int y;
 public :
     point ()
     {
         x=y=;
     }
     point (int a,int b)
     {
         x=a;
         y=b;
     }
     ~point (){}
     void show ()
     {
         cout <<"("<<x<<","<<y<<")"<<endl;
     }
 };
 class Shape
 {
 private:
     double longth;
     double width;
 public :
     Shape ()
     {
         longth=width=;
     }
     Shape (double l,double w)
     {
         longth=l;
         width=w;
         cout<<"构造函数，创建Shape"<<endl;
     }
     ~Shape()
     {
         cout <<"析构函数，释放Shape"<<endl;
     }
     double area()
     {
         double s;
         s=longth*width;
         return s;
     }
     void show ()
     {
         cout <<"面积="<<area()<<endl;
     }
 };
 class Rectangle:public Shape
 {
 public :
     Rectangle():Shape(,){}
     Rectangle(double a,double b):Shape(a,b)
     {
         cout<<"创建Rectangle"<<endl;
     }
     void show ()
     {
         cout <<"面积="<<area()<<endl;
     }
     ~Rectangle()
     {
         cout <<"析构函数，释放Rectangle"<<endl;
     }
 };
 class Square:public Rectangle
 {
 public :
     Square(double a):Rectangle(a,a)
     {
         cout<<"构造函数，创建Square"<<endl;
     }
     ~Square()
     {
         cout <<"析构函数，释放Square"<<endl;
     }
 };
 class Circle:public Shape
 {
 private :
     double r;
     point p;
 public :
     Circle(double c,point n):Shape(c,c)
     {
         r=c;
         p=n;
         cout<<"构造函数，创建Circle"<<endl;
     }
     ~Circle()
     {
         cout <<"析构函数，释放Circle"<<endl;
     }
     double area()
     {
         double s;
         s=3.14*r*r;
         return s;
     }
     void show ()
     {
         cout <<"面积="<<area()<<endl;
     }
 };
 int main()
 {
     Rectangle r(,);
     r.show();
     point o(,);
     Circle c (4.0,o);
     c.show ();
     Square s();
     s.show();
     return ;
 }