基于point为基类的点—圆—圆柱体类的层次结构的改写，在程序中使用虚函数和抽象基类。类的层次结构的顶层是抽象基类Shape(形状)。Point(点), Circle(圆), Cylinder(圆柱体)都是Shape类的直接派生类和间接派生类。-Point for the base class based on points- round- cylinder class hierarchy rewritten, in a program using virtual functions and a