Please help - Linked List

[jenbren]

Hi - I am desperately trying to finish my project and I cannot get the "insert" function to work properly. Basically, the function is going to receive a string dataVal and an index where the code needs to "insert" this item into the linked list. Below is my code - it doesn't work and i'm going nuts. Any help would be so very appreciated!

Thanks


void List::insert( ElementType dataVal, int index )

{
Node *newpointer = new Node();

if (index < 0 || index > size)
{
cout << "Error: Illegal insert position" << endl;
return;
}

Node * predPtr = NULL;

if ( index == 0)
{
return;
}


predPtr = first;

for ( int i = 1; i < index; i++)
{
predPtr = predPtr->next;
}

if (predPtr != 0)

{
newpointer->next = first->next;
first-> next = newpointer;
size++;

}

else
{
newpointer->next = first;
first = newpointer;
size++;

}

}

[coder777]

It looks like you want to insert the value at a specific index.

This

newpointer->next = first->next;
first-> next = newpointer;
size++;

inserts it always after the first element. Use predPtr instead.

I'd expect this

newpointer->next = first;
first = newpointer;
size++;

within that if ( index == 0) clause. if (first == 0) there too?

If 'predPtr' is 0 is either an error (insert an element at the inappropriate place) or you need the last element and simply add it.

You also need to check whether 'first' is 0

[jenbren]

Thank you so much - I really appreciate it. Can you please look at my delete function? I am to delete a value at a given index. I have code below but for some reason, it will not always delete (sometimes it works sometimes it does not).


void List::erase( int index )

{

if (index < 0)
cout << "Invalid index specified";

if (first == NULL)
cout << "No element at specified location";

Node *temp, *newpointer;

temp = first;

if (index == 0)

{
delete first;
}

if (index == 1)

{
temp->next = NULL;

}

else
{
Node *temp;
temp = newpointer->next;
delete temp;

}


}


Thanks so much again!!!

Jen

[coder777]

Well, erase is very much like insert. the if clause and the loop. Just where you link in insert unlink it in erase. Don't forget Size--