说明：  摘自一本书中的VC++ 6.0开发环境下的案例，有详细的全过程讲述如何实现双视图计算器（科学型和标准型）MFC应用程序。
(From a book in the VC++ 6.0 development environment case, the whole process in detail about how to achieve the dual view calculator (scientific type and standard type) MFC application.)