You need to be careful with C's tolower. It takes a signed integer, and negative values are undefined behaviour. It would be safer to cast to unsigned char befo

You need to be careful with C's tolower. It takes a signed integer, and negative values are undefined behaviour. It would be safer to cast to unsigned char before calling tolower. https://en.cppreference.com/w/cpp/string/byte/tolower https://en.cppreference.com/w/cpp/string/byte/tolower