Ah right thanks lol; also noted!

Note that it is undefined behavior to use the ctype.h functions with a char, these functions are supposed to take unsigned chars as arguments

Ah okie noted!
Thankyou very much for making me aware of this, I did not know.
I shall keep this in-mind for future code where such functionality is required :3

You should avoid the use of the ctype.h header and its functions like tolower. The behavior of these functions can change based on locale. It's not an issue here since the tests run on the server with the same locale, but it's a problem when running code on other computers. You can either change the locale using setlocale, or write your own tolower.