Why can't my link list find integers 7 and 8??

Code:

#include <iostream>
#include <vector>
//#include <list>
using namespace std;

struct Node
{
	int data; 

	Node *next;
	
	Node(int d, Node *n) : data(d), next(n)
	{}
};


class List
{
public:

	List()
	{
		head = new Node(int(), NULL);
		//cout << "int() is: " << int() << endl;
	
	}
	
	void Add(int dataX, Node &n1)
	{

		Node *it = head; 

		/*if(it->next != NULL)
		{
			head = new Node(dataX, it->next); 

			head->data = dataX; 
			//cout << "head->data is: " << head->data << endl;
			head->next = NULL; 

			tail = new Node(dataX, it->next); 
		
			tail->data = dataX;
			//cout << "tail->data is: " << tail->data << endl;
			tail->next = NULL; 
				return; 
		}*/

		if(it->next == 0)
		{
			// can't find 7 or 8 due to a problem in here.
			n1.data = it->data;
			//n1.next = it->next;
			cout << "yes, this is definately working" << endl;
			cout << n1.data << endl;
		}

		


		while(it->next != 0)// && it->next->data < dataX)
		{
			int ggg = 0;
			//cout << ++ggg << "this number" << endl;

			n1.data = it->data;
			n1.next = it->next;
		//	cout << n1 << " and " << n1.data << endl;
			it = it->next;
			//cout << "hello world" << endl;
			cout << it->data << endl;
			
			//it->next = new Node(dataX, it->next);

		}

		//cout << "it->data is: " << it->data << endl;

		//if(it->next == NULL)
		//n1->data = dataX;
		//n1 = it->next;
		it->next = new Node(dataX, it->next);
		
			
		

		
		//head = it;

			

		



	}


	bool Count(int y)
	{
		//cout << vTail[-1] << endl;
		return 1;
	
	}

	void RemoveAll(int z)
	{
		Node *it = head;
		//cout << "head->next is right now: " << head->data << endl;
		//cout << "it->next is right now: " << it->data << endl;

		//while(it->next == NULL) // && it->next->data < z)
		//{
			//cout << "hola" << endl;
			it = it->next;

		//	cout << "hola " << it->next << endl;
		//}
		//if(head->next != 0)
		//{
			//Node *it = head->next;
		//	Node *hold = it->next;
		//	it->next = hold->next;

		//	delete hold;

		//	while(it != 0)
		//	{
				//cout << "now it's: " << it->data << "->" << endl;

		//		it = it->next;
		//	}

		//}

		if(it->next != NULL)
		{
			cout << "yes this works" << endl;
			Node *hold = it->next;
			it->next = hold->next;
			//cout << "hold->next is: don't expect to print->: " << hold->next << endl;
			

			delete hold;

			//cout << "hold->next is now: " << hold->data << endl;
			
			//cout << "while remove, it->data is: " << it->data << endl;
		}

		//cout << "after remove, it->data is: " << it->data << endl;
	
	}

	int Contains(int b)
	{
		return 1;
	}


	void display()
	{
		//cout << "head->next in walk is: " << head->data << endl;
		if(head->next != 0)
		{
			Node *it = head->next;

			while(it != 0)
			{
				cout << it->data << "->";

				it = it->next;
				//cout << it->data << "->";
			}

		}

	}





private:
	Node *head;
	Node *tail;

	//List *pNext;

	vector<int> vHead;
	vector<int> vTail;


};

Node *find_entry(Node *lptr, int match)
{
	while(lptr != 0)
		if(lptr->data == match)
		{
			cout << "match is: " << match << endl;
			return(lptr);
		}
		else
			//cout << "lptr->data is: " << lptr->data << endl;
			lptr = lptr->next;

		return (0);

}




int main()
{
	List list;


	Node *find_entry(Node *lptr, int match);
	//Node n1, n2, n3;
	Node *lptr, *list_start;
	//Node n1(NULL, NULL) = &list_start;
	int i, search;
	
	//cout << list.Count(9) << endl; //this should print 0

	list.Add(7, *list_start);
	list.Add(8, *list_start);
	list.Add(9, *list_start);
	list.Add(10, *list_start);
	list.Add(11, *list_start);

	cout << "list start is: " << list_start->data << endl;
	list.display();

	cout << "Enter a value to locate: ";
	cin >> search;

	lptr = find_entry(list_start, search);
	//cout << "this is important: " << lptr->data << endl;

	if(lptr != 0)
		cout << "found " << lptr->data << "." << endl;
	else
		cout << "Not found" << endl;



	list.RemoveAll(7);
	list.RemoveAll(10);
	list.RemoveAll(9);
	list.display();

	//list.Add(7)->head;


	//lptr = list.FindEntry(list_start, match);

	/*if(lptr != 0)
		cout << "Found: " << lptr->data << endl;
	else
		cout << "Not found!" << endl;*/

	

	//cout << list.Add() << endl;

	/*if(list.Contains(12))
		cout << "Found 12" << endl; //this should print
	else
		cout << "Error" << endl;

	if(!list.Contains(15))
		cout << "Did not find 15" << endl; //this should print
	else
		cout << "Error" << endl;*/

	//for(int dataX = 0; dataX < 10; dataX++)
	//	list.Add(dataX);
	
	//cout << list.Count(7) << endl; //should print 2, since there are 2 7's in the list
	
	list.RemoveAll(0);
	
	//cout << list.Count(7) << endl; //should print 0

	cout << endl;

	return 0;
}

in my link list, I'm inserting the integers 7, 8, 9, 10, and 11.

I have a search function: "find_entry" under class list.

This function can find the 9, 10, and 11 that I inserted into my list, but it can't find 7 or 8.

The problem lies within class List, member function Add, somewhere inside the first if statement.

I don't know why n1.data isn't getting assigned to it->data correctly.

Could someone please point me in the right direction?

Thanks

Code:

Node *lptr, *list_start;

list.Add(7, *list_start);

You have a pointer to head already stored in the object list, so why is list_start?

You can use memberfunction Add() just like this:

list.Add (7);

Since the object itself stores head and tail, you don't need to do that in main().

BTW, list_start is a pointer to Node, it is not an object of type Node. So you cannot store data in it. To use it, you would first have to allocate memory for it.