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

  Returns a nonzero integer if its argument is classed as an
  alphabetic character in the program's current locale.  Otherwise,
  it returns 0.

  Syntax:

       #include <ctype.h>

       int isalpha(int character);