Thread: Confusion with a Deque program

I have created a deque program that is supposed to read in the information from a separate program, and if something goes wrong along the way, it returns "Error". Checking each if statement individually, it seems like my error occurs at if

Code:

(!q1.empty())

.

I've looked at this several times, but still cannot find the source of the problem. Here's the application:

Code:

int main(int argc, char *argv[])
{
  Deque q1;  
  int i;

  q1 = Deque();

  q1.append_rear(2);
  q1.append_front(1);
  q1.retrieve_front(i);
  if (i != 1)
    cout << "Error" << endl;
  q1.serve_front();
  q1.retrieve_front(i);
  if (i != 2)
    cout << "Error" << endl;
  q1.serve_rear();
  if (!q1.empty())
    cout << "Error" << endl;
  cout << "DONE" << endl;


  return 0;

Also, this is the program it reads the information from. I assume this is the source of the problem:

Code:

#include "Deque.h"
#include <cassert>

Deque::Deque()
  /*
    Post: The Deque is initialized to be empty.
  */
{
	front = 0;
	rear = 0; 
}


bool Deque::empty() const
  /*
    Post: Return true if the Deque is empty, otherwise return false.
  */
{
	if (front == NULL)
	{
		return true;
	}
	return false;
}


Error_code Deque::append_front(const Deque_entry &item)
  /*
    Post: item is added to the front of the Deque. If the Deque is full
    return an Error_code of overflow and leave the Deque unchanged.
  */
{	
	Error_code o;
	Node *newFront = new Node;
	assert (newFront);
	newFront->entry = item;
	newFront->previous = NULL;

	if (front == NULL)
	{
	  front = newFront;
	  rear = newFront;

	  newFront->next = NULL;
	}

	else  //there are already nodes in the program
	{
		newFront->next = front;
		front->previous = newFront;
		front = newFront;
	}

	if (item > 1)
	{ 
		o = overflow;
		return overflow;
	}

}

Error_code Deque::append_rear(const Deque_entry &item)
  /*
    Post: item is added to the rear of the Deque. If the Deque is full
    return an Error_code of overflow and leave the Deque unchanged.
  */
{	
	Error_code o;
	Node *newRear = new Node;
	assert (newRear);
	newRear->entry = item;
	newRear->next = NULL;

	if (front == NULL)
	{
	  front = newRear;
	  rear = newRear;

	  newRear->previous = NULL;
	}

	else 
	{ 
		rear->next = newRear;
		newRear->previous = rear;
		rear = newRear;
	}

	if (item > 2)
	{ 
		o = overflow;
		return overflow;
	}
}



Error_code Deque::serve_front()
  /*
    Post: The front of the Deque is removed. If the Deque
    is empty return an Error_code of underflow.
  */
{
	Node *p;
	p = front;
	Error_code u;

	if (front == NULL)
	{
		u = underflow;
		return underflow;
	}

	else
	{
		front = front->next;
		delete p;
		return front;
	}
	
}

Error_code Deque::serve_rear()
  /*
    Post: The rear of the Deque is removed. If the Deque
    is empty return an Error_code of underflow.
  */

{
	Node *p;
	p = rear;
	Error_code u;

	if (rear == NULL)
	{
		u = underflow;
		return underflow;
	}

	else
	{
		rear = rear->previous;
		delete p;
	}
}

Error_code Deque::retrieve_front(Deque_entry &item) const
  /*
    Post: The front of the Deque retrieved to the output
    parameter item. If the Deque is empty return an Error_code of underflow.
  */

{	
	Error_code u;
	
	if (front == NULL)
	{
		u = underflow;
		return underflow;
	}

	item = front->entry;
}

Error_code Deque::retrieve_rear(Deque_entry &item) const
  /*
    Post: The rear of the Deque retrieved to the output
    parameter item. If the Deque is empty return an Error_code of underflow.
  */
{
	
	Error_code u;
	if (front == NULL)
	{
		u = underflow;
		return underflow;
	}

	item = rear->entry;

}

Any idea what I may be doing wrong? Perhaps I'm doing it right and I'm just paranoid? If you need to see other files (such as header files), I can provide that, too.

Thanks for any help ahead of time.