// carqueue.h: the CarQueue class, representing the lineup of cars at the
// gas station.

class CarQueue {
private:

   // QueueItem: the type for objects stored in the car queue.
   struct QueueItem {
      // The car queue is a linked list, so each item contains a data field
      // and a "next item" field.
      Car *data;
      QueueItem *next;
   };

   QueueItem *firstWaitingCar;
   QueueItem *lastWaitingCar;
   int queueSize;
   double totalEmptyQueueTime;

public:

   // Constructor.
   // The list of "name (value)" pairs after the colon and before the
   // constructor body provides initial values for those data members.
   CarQueue () : firstWaitingCar (0), lastWaitingCar (0), queueSize (0),
      totalEmptyQueueTime (0.0) { }

   // getEmptyTime: return the total time the car queue has been empty.
   double getEmptyTime ();

   // getQueueSize: return the number of cars in the car queue.
   int getQueueSize () { return queueSize; }

   // insert: put a newly-arrived car into the car queue.
   void insert (Car *newestCar);

   // takeFirstCar: remove first car from car queue and return it.
   Car *takeFirstCar ();
};