VMS Help CC, Run-time functions, tolower, _tolower  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Convert their argument, a character, to lowercase.  If the argument
  is not an uppercase character, it is returned unchanged.

  Syntax:

       #include <ctype.h>

       int tolower(int character);
       int _tolower(int character);