c语言字符串大小写转换

https://www.programmingsimplified.com/c/program/c-program-change-case

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/strlwr-s-strlwr-s-l-mbslwr-s-mbslwr-s-l-wcslwr-s-wcslwr-s-l?view=vs-2019