The
toupper();
function converts a lower-case letter to the corresponding
upper-case letter.
The
_toupper();
function is identical to
toupper();
except that
c
must be a lower-case letter.
RETURN VALUES
If the argument to the
toupper();
function is a lower-case letter, the corresponding upper-case letter
is returned if there is one; otherwise the argument is returned unchanged.
If the argument to the
_toupper();
function is a lower-case letter, the corresponding upper-case letter
is returned; otherwise the output is undefined.