Return value is non-zero for true, 0 for false:

  int isalnum(int)      Tests for any character for which isalpha() or
                        isdigit() is true (letter or digit).

  int isalpha(int)      Tests for any character for which isupper() or
                        islower() is true.

  int iscntrl(int)      Tests for any "control character" as defined by the
                        character set.

  int isdigit(int)      Tests for any decimal-digit character.

  int isgraph(int)      Tests for any  character  for  which  ispunct(),
                        isupper(), islower(), or isdigit() is true.

  int islower(int)      Tests for any character that is a lower-case letter.

  int isprint(int)      Tests for any  character  for  which  ispunct(),
                        isupper(), islower(), isdigit(), or the space
                        character (' ') is true.

  int ispunct(int)      Tests for any printing character which is neither a
                        space (' ') nor a character for which isalnum() or
                        iscntrl() is true.

  int isspace(int)      Tests for any space, tab, carriage-return, newline,
                        vertical-tab or form-feed (standard white-space characters).

  int isupper(int)      Tests for any character that is an upper-case letter.

  int isxdigit(int)     Tests for any hexadecimal-digit character ([0-9],
                        [A-F], or [a-f]).


  int isblank(int)      Tests for a blank character; that is, a space or a tab.


Return value is the original or translated character:

  int tolower(int)      Translate an upper-case character to lower-case.

  int toupper(int)      Translate a lower-case character to upper-case.