2．设计编写大小写字母转换程序实验，要求：

①程序有友好的运行界面；

②接收键盘输入字符，将其中的大小写字母相互转换为，其他非字母符号不变；

③要求程序有方便的输入输出功能；

④要求程序能够处理基本的错误信息；

-2 design and write letters conversion program, requirements:



The program has a friendly operation interface



② receive keyboard input characters, the letters are converted to, other non alphabetic symbols



The required procedures with input and output functions and convenient



The program can handle the basic requirements of the error message