tolower

int tolower(int c)

Returns the lowercase version of c. If c is not an ASCII letter, it is returned unchanged.

To change the case of a whole string, use StrToLower.

tolower('A') -> 'a'
tolower('a') -> 'a'
tolower('/') -> '/' // not a letter
tolower('Ä') -> 'Ä' // non-ASCII character

toupper