My Delphi is pretty hazy, but as far as I know a char is assignment compatible with a string, so StringVar := CharVar should work directly. For string to char I assume the string is one character long, I believe something like PChar(StringVar)^ would work.

My Delphi skills were questionable at the best of times, and I haven't used the language for the better part of a year so it's possible everything I just said is utter crap.