isupper —
upper-case character test
Standard C Library (libc, -lc)
#include <ctype.h>
int
  
  isupper(int
    c);
The isupper() function tests for any upper-case letter
  or any of an implementation-defined set of characters for which none of
  iscntrl(3),
  isdigit(3),
  ispunct(3), or
  isspace(3) is true. In the
  ``C'' locale, isupper() returns true
  only for the characters defined as upper-case letters.
The isupper() function returns zero if the character
  tests false and returns non-zero if the character tests true.
ctype(3),
  isalnum(3),
  isalpha(3),
  isascii(3),
  isblank(3),
  iscntrl(3),
  isdigit(3),
  isgraph(3),
  islower(3),
  isprint(3),
  ispunct(3),
  isspace(3),
  isxdigit(3),
  stdio(3),
  toascii(3),
  tolower(3),
  toupper(3),
  ascii(7)
The isupper() function conforms to ANSI
  X3.159-1989 (“ANSI C89”).
The argument to isupper() must be
  EOF or representable as an unsigned
  char; otherwise, the behavior is undefined. See the
  CAVEATS section of
  ctype(3) for more details.