程序采用菜单式选择，可以接收用户从键盘输入的五个命令（1-5），各命令功能分别为：（1）按下“1”键，完成字符串小写字母变成大写字母（2）接收用户输入的可显示字符串（以回车结束），程序将其中ASCII码值最大的字符显示出来（3）按下“3”键，完成排序（二选一）（4）按下“4”键，显示时间（5）按下“5”键，结束程序运行，返回系统提示符-Program uses menu-driven options, the user can receive commands from the keyboard of the five (1-5), the command functions are: (1) Press " 1"　key to complete the string into uppercase letters lowercase letters (2) receiving user input to display a string (the end of a carriage return), the program will be one of the largest value of ASCII character code shown (3) Press " 3"　key to complete the order (check one) (4) Press " 4 " key to display the time (5) Press"　5 " key to end the run, return to the system prompt