Question

//This is the implementation file queue.cpp.
//This is the implementation of the template class Queue.
//The interface for the template class Queue is in the header file queue.h.

#include <iostream>
#include <cstdlib>
#include <cstddef>
#include "queue.h"
using std::cout;


namespace QueueSavitch
{

//Uses cstddef:
template<class T>
Queue<T>::Queue( ) : front(NULL), back(NULL)
{
    //Intentionally empty.
}

//Uses cstddef:
template<class T>
bool Queue<T>::isEmpty( ) const
{
    return (back == NULL);//front == NULL would also work
}

//Uses cstddef:
template<class T>
void Queue<T>::add(T item)
{
    if (isEmpty( ))
       front = back = new Node<T>(item, NULL);//sets both
                  //front and back to point to the only node
   else
   {
       back->setLink(new Node<T>(item, NULL));
       back = back->getLink( );
   }
}

//Uses cstdlib and iostream:
template<class T>
T Queue<T>::remove( )
{
    if (isEmpty( ))
    {
        cout << "Error:Removing an item from an empty queue.\n";
        exit(1);
    }

    T result = front->getData( );

    Node<T> *discard;
    discard = front;
    front = front->getLink( );
    if (front == NULL) //if you removed the last node
        back = NULL;

    delete discard;

    return result;
}

template<class T>
Queue<T>::~Queue( )
{
    T next;
    while (! isEmpty( ))
       next = remove( );//remove calls delete.
}

//Uses cstddef:
template<class T>
Queue<T>::Queue(const Queue<T>& aQueue)
{
    if (aQueue.isEmpty( ))
        front = back = NULL;
    else
    {
        Node<T> *temp = aQueue.front;//temp moves
        //through the nodes from front to back of aQueue.

        back = new Node<T>(temp->getData( ), NULL);
        front = back;
        //First node created and filled with data.
        //New nodes are now added AFTER this first node.

        temp = temp->getLink( );//temp now points to second
                //node or NULL if there is no second node.

        while (temp != NULL)
        {
            back->setLink(new Node<T>(temp->getData( ), NULL));
            back = back->getLink( );
            temp = temp->getLink( );

        }
        //back->link == NULL
    }
}

//Uses cstddef:
template<class T>
Queue<T>& Queue<T>::operator =(const Queue<T>& rightSide)
{
    if (front == rightSide.front)//if the queues are the same
        return *this;
    else //send left side back to freestore
    {
        T next;
        while (! isEmpty( ))
            next = remove( );//remove calls delete.
    }

    if (rightSide.isEmpty( ))
    {
        front = back = NULL;
        return *this;
    }
    else
    {
        Node<T> *temp = rightSide.front;//temp moves 
          //through the nodes from front to back of rightSide.

        back = new Node<T>(temp->getData( ), NULL);
        front = back;
        //First node created and filled with data.
        //New nodes are now added AFTER this first node.

        temp = temp->getLink( );//temp now points to second
                   //node or NULL if there is no second node.

        while (temp != NULL)
        {
            back->setLink(
                     new Node<T>(temp->getData( ), NULL));
            back = back->getLink( );
            temp = temp->getLink( );
        }
        //back->link == NULL;

        return *this;
    }
}

}//QueueSavitch

Question: Modify the code above to include the function count(). This function shall return an integer value representing the number of nodes in the queue. The function does not display the value only returns the value to the caller. Also modify main() to make use of this function when there are no nodes as well as when there is one node and many nodes.

Answer 1

• It should have been easier, if queue.h file is provided.
• Based on the implementation, I have created queue.h file and added count function.
• Main function uses menu option to test the count functionality.
• All the functions are self explanatory and provided inline comments appropriately.

queue.h file

//file queue.h.
#ifndef QUEUE_H
#define QUEUE_H

//Declare namespace
namespace QueueSavitch
{
template<class T>
class Node
{
public:
Node(T theData, Node<T>* theLink) : data(theData), link(theLink){}
Node<T>* getLink( ) const { return link; }
const T getData( ) const { return data; }
void setData(const T& theData) { data = theData; }
void setLink(Node<T>* pointer) { link = pointer; }
private:
T data;
Node<T> *link;
};

template<class T>
class Queue
{
public:
//Constructor
Queue( );
Queue(const Queue<T>& aQueue);
//Operator overload
Queue<T>& operator =(const Queue<T>& rightSide);
//destructor
virtual ~Queue( );
//Add an item
void add(T item);
//Remove an item
T remove( );
//Returns true if Queue is empty
bool isEmpty( ) const;

//Returns total number of elements in Queue.
//returns zero, if queue is empty
int count() const;
private:
Node<T> *front;
Node<T> *back;
};

}//QueueSavitch

#endif //QUEUE_H

queue.cpp file

#include <iostream>
#include <cstdlib>
#include <cstddef>
#include "queue.h"
using std::cout;

namespace QueueSavitch
{

//Uses cstddef:
template<class T>
Queue<T>::Queue( ) : front(NULL), back(NULL)
{
//Intentionally empty.
}

//Uses cstddef:
template<class T>
bool Queue<T>::isEmpty( ) const
{
return (back == NULL);//front == NULL would also work
}

//Uses cstddef:
template<class T>
void Queue<T>::add(T item)
{
if (isEmpty( ))
front = back = new Node<T>(item, NULL);//sets both
//front and back to point to the only node
else
{
back->setLink(new Node<T>(item, NULL));
back = back->getLink( );
}
}

//Uses cstdlib and iostream:
template<class T>
T Queue<T>::remove( )
{
if (isEmpty( ))
{
cout << "Error:Removing an item from an empty queue.\n";
exit(1);
}

T result = front->getData( );

Node<T> *discard;
discard = front;
front = front->getLink( );
if (front == NULL) //if you removed the last node
back = NULL;

delete discard;

return result;
}

template<class T>
Queue<T>::~Queue( )
{
T next;
while (! isEmpty( ))
next = remove( );//remove calls delete.
}

//Uses cstddef:
template<class T>
Queue<T>::Queue(const Queue<T>& aQueue)
{
if (aQueue.isEmpty( ))
front = back = NULL;
else
{
Node<T> *temp = aQueue.front;//temp moves
//through the nodes from front to back of aQueue.

back = new Node<T>(temp->getData( ), NULL);
front = back;
//First node created and filled with data.
//New nodes are now added AFTER this first node.

temp = temp->getLink( );//temp now points to second
//node or NULL if there is no second node.

while (temp != NULL)
{
back->setLink(new Node<T>(temp->getData( ), NULL));
back = back->getLink( );
temp = temp->getLink( );

}
//back->link == NULL
}
}

//Uses cstddef:
template<class T>
Queue<T>& Queue<T>::operator =(const Queue<T>& rightSide)
{
if (front == rightSide.front)//if the queues are the same
return *this;
else //send left side back to freestore
{
T next;
while (! isEmpty( ))
next = remove( );//remove calls delete.
}

if (rightSide.isEmpty( ))
{
front = back = NULL;
return *this;
}
else
{
Node<T> *temp = rightSide.front;//temp moves
//through the nodes from front to back of rightSide.

back = new Node<T>(temp->getData( ), NULL);
front = back;
//First node created and filled with data.
//New nodes are now added AFTER this first node.

temp = temp->getLink( );//temp now points to second
//node or NULL if there is no second node.

while (temp != NULL)
{
back->setLink(
new Node<T>(temp->getData( ), NULL));
back = back->getLink( );
temp = temp->getLink( );
}
//back->link == NULL;

return *this;
}
}

//New function Count to return number of elements in queue
//Uses cstddef:
template<class T>
int Queue<T>::count() const
{
//Check if queue empty, if so, return zero
if (isEmpty( ))
return 0;
else
{
//Traverse the queue with front element
Node<T> *current = front;
  
//Intialize temp count to store number of elements
//Since we have front, initialize it to 1
int noofelements = 1;
while(current!=back)
{
//we have back element so increase the count by 1.
noofelements++;
//Go to the next element
current= current->getLink( );
}
//Return the counf
return noofelements;
}
}

}//QueueSavitch

Main.cpp

#include <iostream>
#include "queue.h"
#include "queue.cpp"
using std::cin;
using std::cout;
using std::endl;
//Using the Queue namesapce
using QueueSavitch::Queue;

//Display menu
void printmenu()
{
cout<< "******* MENU *******\n";
cout<< "1. Get Total Elements in Queue\n";
cout<< "2. Add new integer to Queue\n";
cout<< "3. Quit\n";
}

//get user choice
int getChoice()
{
int choice;
cout<< "\nEnter your choice (1-3): ";
cin >> choice;
return choice;
}

//get input for queue
int getQueueInput()
{
int queueinput;
cout<< "\nEnter a integer: ";
cin >> queueinput;
return queueinput;
}

//Main method
int main( )
{
//Declare a INT queue
Queue<int> MyQueue;
  
//user input choice
int choice;
do
{
//Print menu
printmenu();
//Get user choice
choice = getChoice();
switch(choice)
{
//Display count
case 1:
{
cout<<"Total elements in Queue: " << MyQueue.count() << "\n";
break;
}
//Add an integer to queue
case 2:
{
int queueinput = getQueueInput();
MyQueue.add(queueinput);
break;
}
//Quit
case 3:
{
cout<<"Good Bye! See you soon!";
}
}
}while(choice != 3); //Quit
return 0;
}

Sample Output:

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