bool Queue empty()const; Post: Return true if the Queue is empty, otherwise return false Extended Queues class Extended queue: public Queue i public: bool full()const; int size const void clear; Error code serve and retrieve Queue entry &itembool Queue :: empty( ) const; Post: Return true if the Queue is empty, otherwise return false. Extended Queues class Extended queue: public Queue { public: bool full( ) const; int size( ) const; void clear( ); Error_code serve and retrieve(Queue entry &item); };