T dequeue() //removeBack
     {
         if (head == NULL) //empty
         {
             return NULL;
         }
         else if (head->next == NULL) //only one item
         {
            T output;
            output = head->data;
            head = NULL;
            delete head;
            return output;
         }
         else
         {   T output;
             temp = tail;
             output = tail->data;
             tail = temp->prev;
             tail->next = NULL;
             delete temp; //ERROR OCCURS HERE
             //tail->next = NULL;
             return output;

         }
     }