声明一个基类Shape（点）, 在此基础上派生出Rectangle（长方形）和Circle（圆）,这三个类都有GetArea()函数计算对象的面积,构造函数，析构函数等有关函数。再使用Rectangle类创建一个派生类Square(正方形)。并设计创建各种类的对象，调用所有函数。设计函数f(Shape &a)能对不同对象的实参调用计算打印出对象的面积。

-statement a base class Shape (points) On this basis-- for Rectangle (rectangular) and Circle (Yuen), This category has three GetArea () function calculation of the area of the object, Constructors and destructor function and other functions. Rectangle re-use categories to create a derived class Square (square). Design and creation of all the different types of targets, calling all functions. Design function f (Shape