I have never used strings in Arduino before so forgive me if I say something wrong.
and you aren't using them now.
There is a very important distinction to be made between Strings (capital S) and strings (lowercase s)
A String is an object created using the String library. Using them can fragment memory causing bugs that are difficult to track down. This is exacerbated by the limited amount of memory available on most Arduinos.
A string is a zero terminated array of chars. Using them causes no memory fragmentation