Go forward to isupper
Go backward to ispunct
Go up to Ctype
Go to the top op libc

`isspace'--whitespace character predicate

     #include <ctype.h>
     int isspace(int C);
`isspace' is a macro which classifies ASCII integer values by table
lookup.  It is a predicate returning non-zero for whitespace
characters, and 0 for other characters.  It is defined only when
`isascii'(C) is true or C is EOF.
   You can use a compiled subroutine instead of the macro definition by
undefining the macro using ``#undef isspace''.
`isspace' returns non-zero if C is a space, tab, carriage return, new
line, vertical tab, or formfeed (`0x09'-`0x0D', `0x20').
`isspace' is ANSI C.
   No supporting OS subroutines are required.