c/string/byte/isupper

Checks if the given character is an uppercase character according to the current C locale. In the default "C" locale, returns true only for the uppercase letters.

If returns, it is guaranteed that iscntrl, isdigit, ispunct, and isspace return  for the same character in the same C locale.

The behavior is undefined if the value of is not representable as  and is not equal to.

Return value
Non-zero value if the character is an uppercase letter, zero otherwise.