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

This is a discussion on Why can't my link list find integers 7 and 8?? within the C++ Programming forums, part of the General Programming Boards category; Code: #include <iostream> #include <vector> //#include <list> using namespace std; struct Node { int data; Node *next; Node(int d, Node ...

  1. #1
    LinkedListQ3
    Guest

    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

  2. #2
    ....
    Join Date
    Aug 2001
    Location
    Groningen (NL)
    Posts
    2,386
    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.

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