Acces violation error with queue and linked list c++ - visual-c++

Question

I have an assignment and it's to build a queue linked list.
Our professor gave us the skeleton and told us to use his main.
I wrote my functions and everything compiled right but when I ran it, I got this error.
Don't know what to do from here.
Source Code:
#include<iostream>
using namespace std;
template<class ItemType>
struct NodeType
{
ItemType info;
NodeType* next;
};
template<class ItemType>
class Queue
{
private:
int size;
NodeType<ItemType>* front; // It points to the front of a singly-linked list
NodeType<ItemType>* rear; // It points to the end of a singly-linked list
public:
Queue(); // default constructor: Queue is created and empty
Queue(const Queue<ItemType> &x); // copy constructor: implicitly called
// for a deep copy
void MakeEmpty(); // Queue is made empty; you should deallocate all
// the nodes of the linked list
bool IsEmpty( ); // test if the queue is empty
bool IsFull( ); // test if the queue is full; assume MAXITEM=5
int length( ); // return the number of elements in the queue
void Print( ); // print the value of all elements in the queue in the sequence
// from the front to rear
void Enqueue(ItemType x); // insert x to the rear of the queue
// Precondition: the queue is not full
void Dequeue(ItemType &x); // delete the element from the front of the queue
// Precondition: the queue is not empty
~Queue(); // Destructor: memory for the dynamic array needs to be deallocated
};
template<class ItemType>
Queue<ItemType>::Queue()
{
size = 0;
front = NULL;
rear = NULL;
}
template<class ItemType>
Queue<ItemType>::Queue(const Queue<ItemType> &x)
{
NodeType<ItemType>* ptr1 ;
NodeType<ItemType>* ptr2 ;
if ( x.front == NULL )
{
front = NULL ;
}
else // allocate memory for first node
{
front = new NodeType<ItemType> ;
front->info = x.front->info ;
ptr1 = x.front->next ;
ptr2 = front ;
while ( ptr1 != NULL ) // deep copy other nodes
{
ptr2->next = new NodeType<ItemType> ;
ptr2 = ptr2->next ;
ptr2->info = ptr1->info ;
ptr1 = ptr1->next ;
}
ptr2->next = NULL;
rear = ptr2;
}
}
template<class ItemType>
void Queue<ItemType>::MakeEmpty()
{
NodeType<ItemType>* tempPtr;
while(front != NULL)
{
tempPtr = front;
front = front->next;
delete tempPtr;
}
rear=NULL;
}
template<class ItemType>
bool Queue<ItemType>::IsEmpty()
{
return (size == 0);
}
template<class ItemType>
bool Queue<ItemType>::IsFull()
{
return (size >= 5);
}
template<class ItemType>
int Queue<ItemType>::length()
{
return size;
}
template<class ItemType>
void Queue<ItemType>::Enqueue(ItemType x)
{
NodeType<ItemType>* newNode;
newNode = new NodeType<ItemType>;
newNode->info = x;
newNode->next = NULL;
if(rear == NULL)
{
front = newNode;
}
else
{
rear->next = newNode;
rear = newNode;
}
size++;
}
template<class ItemType>
void Queue<ItemType>::Dequeue(ItemType &x)
{
NodeType<ItemType>* tempPtr;
if(!IsEmpty())
{
tempPtr = front;
x = front->info;
front = front->next;
if(front == NULL)
{
rear = NULL;
}
delete tempPtr;
}
size--;
}
template<class ItemType>
void Queue<ItemType>::Print()
{
NodeType<ItemType> *temp;
temp = rear;
while(temp != NULL)
{
cout<<temp->info<<endl;
temp = temp->next;
}
}
template<class ItemType>
Queue<ItemType>::~Queue()
{
MakeEmpty();
}
int main()
{
Queue<int>IntQueue;
int x;
IntQueue.MakeEmpty();
IntQueue.Dequeue(x);
IntQueue.Enqueue(10);
IntQueue.Enqueue(20);
IntQueue.Enqueue(30);
IntQueue.Enqueue(40);
cout << "int length 3 = " << IntQueue.length() << endl;
IntQueue.Dequeue(x);
cout << "int length 4 = " << IntQueue.length() << endl;
cout << "The int queue contains: " << endl;
IntQueue.Print();
if(IntQueue.IsFull() == false)
cout << "The int queue is not full !" << endl;
else
cout << "The int queue is full !" << endl;
Queue<float>FloatQueue;
float y;
FloatQueue.MakeEmpty();
FloatQueue.Dequeue(y);
FloatQueue.Enqueue(7.1);
cout << "float length 3 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(2.3);
cout << "float length 4 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(3.1);
FloatQueue.Dequeue(y);
cout << "The float queue contains: " << endl;
FloatQueue.Print();
Queue<float> FloatQueue2 = FloatQueue;
cout << "The float queue 2 contains: " << endl;
FloatQueue2.Print();
FloatQueue.MakeEmpty();
cout << "The float queue 3 contains: " << endl;
FloatQueue2.Print();
system("pause");
return 0;
}
The problem I'm having is obviously with the print function.
Any help is appreciated.

Answer 1

Inside your copy constructor, you aren't setting rear to anything when x.front == NULL. This sets temp to an invalid value inside Print, causing you both to loop when you shouldn't and dereference an invalid pointer.