int toupper(int c);

toupper converts a lowercase letter to a corresponding uppercase letter. If the argument is a character for which islower is true and there are one or more corresponding characters, as specified by the current locale, for which isupper is true, toupper returns one of the corresponding characters (always the same one for any given locale); otherwise, the argument is returned unchanged. Note that even though islower can return true for some characters, toupper may return that lowercase character unchanged as there are no corresponding uppercase characters in the locale.