text: #include <ctype.h>
  int isalpha(int c);
  int isblank(int c);
  int isupper(int c);
  int islower(int c);
  int isdigit(int c);
  int isxdigit(int c);
  int isalnum(int c);
  int isspace(int c);
  int ispunct(int c);
  int isprint(int c);
  int isgraph(int c);
  int iscntrl(int c);
  int isascii(int c);
  The macro isascii is defined on all integer values;
  the rest are defined only where the argument is an
  int,
  the value of which is representable as an
  unsigned char,
  or EOF, which is defined by the stdio.h header file
  and represents end-of-file.
  All the character classification macros use a table lookup.
  Functions exist for all the above defined macros.
  To get the function form, the macro name must be bypassed (for example,
  #undef isdigit).