明一个Cat类，拥有静态数据成员HowManyCats，记录Cat的个体数目；声明静态成员函数GetHoMany(),存取HowManyCats。设计程序测试这个类，体会静态数据成员和静态成员函数的用法。-States members GetHoMany () function, access HowManyCats design program test this class, experience static data members and static member functions