Thread: Calculator + LinkedList

i'v tryed to creat new node if fFirst is empty but got a problem to test if fFirst is empty

Code:

void LinkedList::push_back (CalcCommand* data)
{
	
	if (isEmpty())
	{
		fFirst->setNext(data);
	}
	else
	{
		CalcCommand* temp =fFirst;

		while (temp->getNext() != 0)
		{
		    temp = temp -> getNext ();//to let temp point to the last node in the list
		}
		
		temp -> setNext (data);//this will add data to the end of the list
		data -> setNext (0); //and this will set the one after the end of the list to NULL
	}
}

Originally Posted by quzah

Code:

if (isEmpty())
	{
		fFirst->setNext(data);
	}

If this is in fact empty, which by definition means that 'fFirst' is null, then how can you be calling 'fFirst->setNext(data)'? You're trying to access a null pointer there. That's bad.

Quzah.

hi quzah
but it's the same when you creat a new object you set the pointers to NULL then you let them point to what ever

Originally Posted by Stoned_Coder

read xeraths comment. it says it all. You use a list thats not there. fFirts is NULL on first use so temp is also NULL. This is your problem.

yes Stoned_Coder
i think that's it
there is no LinkedList object , so i have to creat it it first , but the my problem now that in the Main function i call Calculator Object ,, but i don't get it to start the program using LinkedList Object
thanks

Code:

void LinkedList::push_back (CalcCommand* data)
{
	
	if (isEmpty())
	{
		fFirst = new Node(...); //this's what's missing
		fFirst->setNext(data);
	}
	else
	{
		CalcCommand* temp =fFirst;

		while (temp->getNext() != 0)
		{
		    temp = temp -> getNext ();//to let temp point to the last node in the list
		}
		
		temp -> setNext (data);//this will add data to the end of the list
		data -> setNext (0); //and this will set the one after the end of the list to NULL
	}
}