Question

I’m a programming student in my first C++ class, and recently we covered linked lists, and we were given an assignment to implement a simple one. I have coded everything but my pop_back() function, which is supossed to return a pointer to the Node that needs to be deleted in Main(). No Node deletion is to be done in the actual function. So my question is:

Would you be willing to help point me in the right direction for my pop_back() function? Also, if you notice anything else that I’m doing wrong, let me know.

Also, this linked list is just to work with strings. In this case, a grocery list, so one string for the quantity of the item(1,2), and one string for the item type. (Milk, Eggs, etc.)

Below I’ve included my List & Node class implementations, so you can get an idea of what I’ve done so far.

Node.cpp

Node::Node(void)
{
    descrip = " ";
    quantity = " ";
    previous = NULL;
    next = NULL;
}
Node::Node(string q, string d)
{
    descrip = d;
    quantity = q;
    previous = NULL;
    next = NULL;
}
Node* Node::GetNext()
{
    return next;
}
Node* Node::GetPrevious()
{
    return previous;
}
void Node::SetNext(Node * setter)
{
    next = setter;
}
void Node::SetPrevious(Node * setter)
{
    previous = setter;
}

---

List.cpp

List::List(void)
{
   first = NULL;
   last = NULL;
   numNodes = 0;
}
Node* List::GetFirst()
{
    return first;
}
Node* List::GetLast()
{
    return last;
}
void List::SetFirst(Node* setter)
{
    first = setter;
}
void List::SetLast(Node* setter)
{
    last = setter;
}
int List::GetNumNodes()
{
    return numNodes;
}
void List::push_front(Node* item)
{
   if (first == NULL)
   {
       first = item;
       last = item;
   }
   else 
   {
       Node* pFirst = first;
       item->SetNext(pFirst);
       first = item;
       numNodes++;
   }
}
void List::push_back(Node * item)
{
    if (last == NULL)
    {
       first = item;
       last = item;
    }
    else 
    {
        last->SetNext(item);
        last = item;
        numNodes++;
    }
}
Node* List::pop_front()
{
    Node* temp = first;
    first = first->GetNext();
    if (first == NULL)
    {
        temp = first->GetNext();
        first = p;
    }
    if (first == NULL)
    {
        last = NULL;
    }
    if (numNodes > 0)
    {
        numNodes--;
    }
    return temp;
}
Node* List::pop_back() // this whole function may be wrong, this is just my attempt at it
{
    Node* temp;
    temp = first;

    while((temp->GetNext()) != NULL)
        // im stuck here

}

Answer 1

So if I understand this right you just want to run through your linked list until you get to the last node in the linked list and return the pointer to it?
I’m pretty sure what you have there will do it except

Node* List::pop_back() // this whole function may be wrong, this is just my attempt at it  
{  
    Node* temp;  
    temp = first;  
    while(temp->GetNext() != NULL)  
    {  
        temp = temp->GetNext();  
    }  
    return temp;  
}

So if I read it right, there it will continually loop around until it gets to the node with none in the line behind it, then return it.