virtual void display() const = 0;

to QueueInterface, add the declaration

void display() const;

to the class declaration in the header file, and add the following method definition to the implementation file:

template<class ItemType>

void LinkedQueue<ItemType>::display() const

{

Node<ItemType>* curPtr = frontPtr;



while (curPtr != backPtr)

{

cout << curPtr->getItem() << " "; // Display items on same line

curPtr = curPtr->getNext();

} // end while

cout << backPtr->getItem() << " "; // Display last item



cout << endl; // Terminate output with an end of line

} // end display