理解和掌握C++抽象类和具体类的实现，了解运算符重载。

实验内容：

　　（1）从Point、Circle类中抽象出基类Shape，研究抽象类和具体类的接口和实现。

　　（2）从中派生出一个正方形类和圆柱体类，然后写一个测试程序，输出正方形的面积和圆柱体的体积。

　　（3）在Circle类中实现关系运算符重载（<、<=、==、!=、>、>=），实现按半径对Circle对象排序。-Understand and grasp the abstract and concrete classes C++ realization understand operator overloading. Experiment: (a) From the Point, Circle class abstract base class Shape, research abstract and concrete classes of interface and implementation. (2) derived from a square cylinder class and the class, and then write a test program, the output square area and volume of a cylinder. (3) In the Circle class operator overloading of relations (< , < =, ==,! =,> ,>　=), To achieve by the radius of the right sort Circle object.