Thread: Simple add to linked list

Hey guys. I have a few years of programming under by belt but I'm new to C++ (coming from mostly Java and C#). I have a linked list that seems to work properly except for the add method. The nodes of the linked list are AdjacencyListNode objects that just have an int (variable name is data) and a pointer (variable name is next) to the next node.

Adding the first node to the list behaves properly. Adding the second node does add a second node, but the data in the node is that of the first. In general there is just some weird behavior going on. I've posted the add method and the part of the program that calls this. The output is below the code. If anyone sees something that is incorrect, please tell me. Thanks for your time guys

Code:

//============================================
// Adds a new node to the beginning of
// the list. Parameter node is the pointer to
// the node that will be added to the list.
//
// PRE:  AdjacencyList with size n is defined
// POST: AdjacencyList with node added to the 
//       front of the list. Length is n + 1.
//============================================
void AdjacencyList::add(AdjacencyListNode * node)
{
	// Check if list is empty
	if (first == NULL)
		first = node;

	else //List not empty 
	{
		//Hook up new node's next
		node->next = first;

		// Set first to new node
		first = node;
         }
		//Increment length
		length++;
}

Here's the part of the main program that calls this:

Code:

	AdjacencyList list;
	list.add(new AdjacencyListNode(2));
	list.display();

	list.add(new AdjacencyListNode(3));
	list.display();

	list.add(new AdjacencyListNode(4));

	list.display();

	cout << list.length << endl;

And finally the output:

Code:

Displaying List:
Node Data: 2
Displaying List:
Node Data: 3
Node Data: 3
Displaying List:
Node Data: 4
Node Data: 4
Node Data: 3
3

Okay. I've posted the related classes below. Thanks again!

Graph.cpp

Code:

//================================================
// Main method
//================================================
int main()
{
	AdjacencyList list;
	list.add(new AdjacencyListNode(2));
	list.display();

	list.add(new AdjacencyListNode(3));
	list.display();

	list.add(new AdjacencyListNode(4));

	list.display();

	cout << list.length << endl;
	return 0;
}

AdjacencyList.h

Code:

#pragma once
#include "AdjacencyListNode.h"

#ifndef ADJLIST_DEF
#define ADJLIST_DEF

class AdjacencyList
{
public:
	int length;					// Size of the list
	AdjacencyListNode * first;		// Pointer to the front of the list
	AdjacencyList();				// Constructor
	void add(AdjacencyListNode *);	// Adds a new node to the front of list
	void display();			        // Displays the nodes of the list 
};
#endif

AdjacencyList.cpp

Code:

#include "StdAfx.h"
#include "AdjacencyList.h"
#include "AdjacencyListNode.h"
#include <iostream>
using namespace std;
//============================================
// Default Constructor for an AdjacencyList
//
// PRE: AdjacencyList is undefined
// POST: AdjacencyList is defined with first
//       set to null and length zero.
//============================================
AdjacencyList::AdjacencyList()
{
	first = NULL;
	length = 0;
}

//=============================================
// Prints the contents of the list.
//
// PRE:  List is defined.
// POST: Contents of the list are printed.
//=============================================
void AdjacencyList::display()
{
	//Temproary node to iterate through the list with
	AdjacencyListNode * tmp;
	tmp = first;

	cout << "Displaying List: " << endl; 
	first->display();

	// Iterate through list and display each node
	while (tmp->next != NULL)
	{
		tmp->display();
		tmp = tmp->next;
	}
}

//============================================
// Adds a new node to the beginning of
// the list. Parameter node is the pointer to
// the node that will be added to the list.
//
// PRE:  AdjacencyList with size n is defined
// POST: AdjacencyList with node added to the 
//       front of the list. Length is n + 1.
//============================================
void AdjacencyList::add(AdjacencyListNode * node)
{
	// Check if list is empty
	if (first == NULL)
		first = node;

	else //List not empty 
	{
		//Hook up new node's next
		node->next = first;

		// Set first to new node
		first = node;
	}
		//Increment length
		length++;
}

AdjacencyListNode.h

Code:

#pragma once
#ifndef ADJNODE_DEF
#define ADJNODE_DEF

class AdjacencyListNode
{
public:
	AdjacencyListNode();			// Creates a new empty node
	AdjacencyListNode(int);		// Creates node with int as data 
	AdjacencyListNode * next;		// Pointer to next item in list
	void display();				// Prints the node's data
	int data;					// Number to identify the node in the
                                                        // graph
};
#endif

AdjacencyListNode.cpp

Code:

#include "StdAfx.h"
#include "AdjacencyListNode.h"
#include <iostream>
using namespace std;
//===========================================
// Default constructor for AdjacencyListNode
//
// PRE:  Node is undefined.
// POST: The node is defined with data set
//		 to -1 and next set to null.
//===========================================
AdjacencyListNode::AdjacencyListNode()
{
	data = -1;
	next = NULL;
}

//=============================================
// Alternate Constructor for AdjacencyListNode. 
// Parameter num is the value for the data to
// be set to.
//
// PRE:  Node is undefined.
// POST: Node is defined with data = num and
//       next set to null.
//=============================================
AdjacencyListNode::AdjacencyListNode(int num)
{
	data = num;
	next = NULL;
}

//===================================
// Displays the node's data
//
// PRE:  Node is defined.
// POST: Node's data is printed.
//===================================
void AdjacencyListNode::display()
{
	cout << "Node Data: " << data << endl;
}

Bingo!! Thanks a lot I figured it was something stupid on my part.