Unhandled Exception Error.. please help

[Zunain]

//cant find what is wrong with the code.. please help guys.. it gives some
//unhandled exception error

#include<iostream>
#include"conio.h"

using namespace std;

class DoublyNode
{
	private:
		int data;
		DoublyNode* nxtPtr;
		DoublyNode* prvPtr;
	public:
		DoublyNode()
		{
			data=0;
			nxtPtr=NULL;
			prvPtr=NULL;
		}
		void setData(int object)
		{
			data=object;
		}
		int getData()
		{
			return data;
		}
		void setNxtPtr(DoublyNode* nextNode)
		{
			nxtPtr=nextNode;
		}
		DoublyNode* getNxtPtr()
		{
			return nxtPtr;
		}
		void setPrvPtr(DoublyNode* prvNode)
		{
			prvPtr=prvNode;
		}
		DoublyNode* getPrvPtr()
		{
			return prvPtr;
		}
};

class DoublyList
{

private:
	DoublyNode* headNode;
	DoublyNode* currentNode;
	int size;

public:
	DoublyList()
	{
		headNode=new DoublyNode();
		headNode->setNxtPtr(NULL);
		headNode->setPrvPtr(NULL);
		currentNode=headNode;
		size=0;
	}

	void add(int object)
	{
		DoublyNode* newNode=new DoublyNode();
		newNode->setData(object);
		if(headNode->getNxtPtr()!=NULL)
		{
			newNode->setNxtPtr(currentNode->getNxtPtr());
			newNode->setPrvPtr(currentNode);
			(currentNode->getNxtPtr())->setPrvPtr(newNode);
			currentNode->setNxtPtr(newNode);
			currentNode=newNode;
		}
		else
		{
			headNode->setNxtPtr(newNode);
			newNode->setPrvPtr(headNode);
			newNode->setNxtPtr(NULL);
			currentNode=newNode;
		}
		size++;
	}

	void remove()
	{
		if(headNode->getNxtPtr()==NULL)
			cout<<"\nThe List is empty";
		else
		{
			if(currentNode->getNxtPtr()!=NULL)
			{
				cout<<"\nList Element "<<currentNode->getData()<<" will be removed now";
				DoublyNode* temp=currentNode;
				(currentNode->getPrvPtr())->setNxtPtr(currentNode->getNxtPtr());
				(currentNode->getNxtPtr())->setPrvPtr(currentNode->getPrvPtr());
				currentNode=currentNode->getNxtPtr();
				delete temp;
			}
			else
			{
				DoublyNode* temp=currentNode;
				(currentNode->getPrvPtr())->setNxtPtr(currentNode->getNxtPtr());
				currentNode=currentNode->getPrvPtr();
				delete temp;
			}
			size--;			
		}
	}

	int find(int object)
	{
		DoublyNode* temp=headNode->getNxtPtr();
		int i=1;
		while(temp!=NULL&&temp->getData()!=object)
		{
			temp=temp->getNxtPtr();
			i++;
		}
		if(!temp) return 0;
		else
		{
			currentNode=temp;
			return i;
		}
		delete temp;
	}

	void start()
	{
		if(headNode->getNxtPtr()!=NULL)
		{
			currentNode=headNode->getNxtPtr();
		}
	}

	int length()
	{
		return size;
	}
	
	int get()
	{
		if(headNode->getNxtPtr()!=NULL&&currentNode!=NULL)
			return currentNode->getData();
	}

	bool next()
	{
		if(currentNode->getNxtPtr()!=NULL)
		{
			currentNode=currentNode->getNxtPtr();
			return true;
		}
		else
			return false;
	}

	bool prev()
	{
		if(currentNode!=headNode->getNxtPtr())
		{
			currentNode=currentNode->getPrvPtr();
			return true;
		}
		else
			return false;
	}

	void display()
	{
		DoublyNode* temp=headNode->getNxtPtr();
		if(temp==NULL)
			cout<<"\nThe List is empty";
		else
		{
			cout<<"\nList:"<<endl;
			while(temp!=NULL)
			{
				cout<<temp->getData()<<",";
				temp=temp->getNxtPtr();
			}
		}
	}
};

int main()
{
	DoublyList a;
	a.display();
	a.add(2);
	a.add(4);
	a.add(7);
	a.add(9);
	a.add(8);
	a.display();

	getch();
	return 0;
}

[MikeyBoy]

1) Please use code tags when posting code, to make it readable:

http://www.cplusplus.com/articles/z13hAqkS/

2) I recommend running your program in a debugger. That will tell you exactly where it's crashing, and allow you to examine the state of the memory to determine what the problem might be.

[Zunain]

I've tried running it in a debugger.. it shows a specific error window which says "Unhandled exception at 0x013C53C9 in DoublyLinkedList.exe: 0xC0000005: Access violation writing location 0x00000008."

[MikeyBoy]

You need to look at the call stack at the point when the exception is thrown, to see where it's happening.

[Zunain]

I dont understand what you are saying o.o

[MikeyBoy]

Do you know what a debugger is, and what features a debugger will provide to help you diagnose problems with your software?

[tanezavm]

Exchange Line 71 and 72. It is a wrong logic if you don't exchange the 2 lines. Since you expect the node next to the current node is not null and you access it. It is yet null since you did not set a valid node next to the current node so null pointer access violation occured