类是程序模块化的一个主要工具，它封装了将一个数据结构和对该数据结构的一组操作

 友员是破坏信息隐蔽的一种机制，主要目的是考虑程序的运行效率

 静态数据成员的作用是在多个模块之间共享数据。静态成员函数提供对静态数据成员操作的封装以及不依赖对象数据的共同操作-Class is a major tool for modular program, which encapsulates a data structure and the data structure of a set of operations is the destruction of information 　Friends of the hidden member of a mechanism, the main purpose is to consider the efficiency of program static data members 　The role is to share data between multiple modules. Provide a static member function static data members of the operation of the package and not dependent on co-operation of object data