pointers reseting

plageiusdarth (2)
I am learning how to use linked lists. When I move from one member function to another the pointers reset to NULL. I thought that having the pointers be global variables should mean that the pointers keep the values they are assigned?


If you have any tips for me, including general tips for linked lists, I would really appreciate it. 

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// SingleLinkedList.h

#include <iostream>
#include <string>

using namespace std;

class Node
{
	private:
		//Pieces of the Node
		string data;
		//string dataSearchable;
		Node* slink;

	public:
		//Special Constructor Thing
		Node ();
		//Member Functions
		bool searchList ();
		void fillNode ();
		void insertNode ();
		void deleteNode ();
		bool clearList ();
		void writeList ();
		//Special Function
		string inputData (string);
		//Pointers
		Node* headptr;
		Node* ptr;
		//Global Variable
		string dataField;
};

Node::Node()
{
	headptr=NULL;
}

bool Node::searchList ()
{
	Node* ptr1;
	ptr1 = headptr;
	cout << "\nPlease input the data string\n";
	cin.ignore(1000, '\n');
	getline (cin, dataField);
	while (ptr1->data != dataField && ptr1 != NULL)
		ptr1 = ptr1 -> slink;
	if (ptr1 -> data == dataField)
	{
		cout << endl << ptr1 -> data << endl;
		return true;
	}
	else
	{
		if (ptr1 = NULL)
		{
			cout << endl << dataField << "is not in the list\n";
			return false;
		}
		else
		{
			cout << endl << "Programmer Error\n";
			return false;
		}
	}
}

void Node::fillNode ()
{
	ptr = new Node;
	cout << "\nPlease input the data string\n";
	cin.ignore(1000, '\n');
	getline (cin, dataField);
	
	ptr -> data = dataField;
	ptr -> slink = NULL;
	
}

void Node::insertNode ()
{
	
	Node* ptr1;
	Node* ptr2;
	ptr1 = headptr;
	if (ptr1 == NULL)
	{
		headptr = ptr;
		ptr -> slink = NULL;
		
	}
	else
	{
		while ((ptr1 -> data <= ptr -> data) && (ptr1 != NULL))
		{
			ptr2 = ptr1;
			ptr1 = ptr1 -> slink;
		}
		
		if (ptr1 -> data > ptr -> data)
		{
			ptr2 -> slink = ptr;
			ptr -> slink = ptr1;
			
		}
		else
		{
			if (ptr1 == NULL)
			{
				ptr2 -> slink = ptr;
				ptr -> slink = NULL;
				
			}
			else
				cout << "\nProgramming Error\n";
		}
	}
}

void Node::deleteNode ()
{
	Node* ptr1;
	Node* ptr2;
	ptr1 = headptr;
	cout << "\nPlease input the data string\n";
	cin.ignore(1000, '\n');
	getline (cin, dataField);
	while (ptr1->data != dataField && ptr1 != NULL)
	{
		ptr2 = ptr1;
		ptr1 = ptr1 -> slink;
	}
	if (ptr1 -> data == dataField)
	{
		ptr2 -> slink = ptr1 -> slinky;
		delete ptr1;
	}
	else
	{
		if (ptr1 == NULL)
		{
			cout << "\nThe data entered is not in the list\n";
		}
		else
		{
			cout << "\nProgrammer Error\n";
		}
	}
}

bool Node::clearList()
{
	Node* ptr1;
	if (headptr == NULL)
	{
		delete headptr;
		return true;
	}
	else 
	{
		do
		{
			ptr1 = headptr;
			headptr = headptr -> slink;
			delete ptr1;
		}
		while (headptr != NULL);
		return true;
	}
	
}

void Node::writeList ()
{
	Node* ptr1;
	
	if (headptr == NULL)
		cout << "\nList is Empty\n";
	else
	{
		ptr1 = headptr;
		while (ptr1 != NULL)
		{
			cout << endl << ptr1 -> data << endl;
			ptr1 = ptr1 -> slink;
		}
	}
}


and the test harness for it

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#include <iostream>
#include "SingleLinkedList.h"
using namespace std;

void switcher (Node);

int b;


int main ()
{
	Node a;
	b=2;
	while (b>1)
		switcher (a);
	cout << "\ngoodbye\n";
	cin.ignore(2);
	return 0;
}

void switcher (Node a)
{
	int switchingNumber;
	cout << "\nPlease Select the Number of the Option You Want.\n";
	cout << "1) Create a New Node.\n" <<
			"2) Print the List.\n" <<
			"3) Search the List.\n" <<
			"4) Delete a Node.\n" <<
			"5) Clear the List.\n" <<
			"6) Exit Program.\n";
	cin >> switchingNumber;
	switch (switchingNumber)
	{
	case 1: a.fillNode ();
			a.insertNode ();
			b = 2;
	break;
	case 2: a.writeList ();
			b = 2;
	break;
	case 3: a.searchList ();
			b = 2;
	break;
	case 4: a.deleteNode ();
			b = 2;
	break;
	case 5: a.clearList ();
			b = 2;
	break;
	case 6: //cout << "switch working";
		b = 0;
			
	break;
	}
}




Thanks
Last edited on
Peter87 (11254)
On line 56 you use = instead of ==.
plageiusdarth (2)
I first noticed the problem when I ran this section
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case 1: a.fillNode ();
			a.insertNode ();
			b = 2;
	break;


though I the problem seems to extend to the rest of the .h library
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