分别用成员和友元方法实现两个复数类相减;定义三个数之间较小者的函数模板;从屏幕上输入若干行数据，把它自动保存在文件中,输入“exit”结束屏幕保存。(Two complex classes are reduced by member and friend method respectively.Defines the function template of the smaller of the three Numbers;Enter a few lines of data from the screen, save it automatically in the file, and enter "exit" to end the screen.)