I need assistance in figuring out how to erase the first element in the linked l

Question

I need assistance in figuring out how to erase the first element in the linked list without giving a stack dump error,  I need to be able to delete the first key without error.  Also with the Insert function, I need to have a check that makes sure I am not adding something that is already in the linked List.  

I have marked where I need help at.  Thanks in advance.

bool LinkedList::erase (const KeyType &key)
{
    NodePointer nptr = first;
    NodePointer ptr  = first;
        while (ptr != NULL)
        {
       ***** NEED HELP HERE*********     if (ptr->data.key == key && ptr == first)
            {
                nptr->next = ptr->next;
                delete nptr;
                return true;
            }
            if (ptr->data.key == key)
            {
                cout <<"-------------------------------------------------------------" << endl;
                cout <<" The following record has been DELETED:" << endl << endl;
                cout <<" Key: " << ptr->data.key << endl;
                cout <<" Title: " << ptr->data.title << endl;
                cout <<" Author: " << ptr->data.author << endl;
                cout <<"-------------------------------------------------------------" << endl;
               
                nptr->next = ptr->next;
                delete ptr;
                return true;
            }
                nptr = ptr;
                ptr = ptr->next;
        }
       
        cout << endl;
            cout << "--------------------------------------------------------" << endl;
            cout << " - Sorry, record not removed because it was not found. -" << endl;
            cout << "--------------------------------------------------------" << endl;   
        return false;
}

void LinkedList::insert(const ElementType &item)
{

    NodePointer cPtr = first;
    NodePointer pPtr = first;
    NodePointer nPtr = new Node(item);
 ***********NEED HELP HERE*************   if (cPtr == nPtr || pPtr == nPtr)
    {
        cout << "sorry but there is already a record with that Unique Key. " << endl;
    }
        if (first == NULL)
        {
            nPtr->next = first;
            first = nPtr;
        }
        else
        {
       
            while(cPtr != NULL && nPtr->data.key >= cPtr->data.key)
            {
                pPtr = cPtr;
                cPtr = cPtr->next;
            }
            if(cPtr == first)
            {
            nPtr->next = first;
            first = nPtr;
            }
            else
            {
            nPtr->next = pPtr->next;
            pPtr->next = nPtr;
            }
        }
   
       
}

Explanation / Answer

Where you say : nptr->next = ptr->next; delete nptr; return true; It looks like your assigning the pointers backwards. You're assigning nptr->next to ptr->next and then deleting it on the next line. Try deleting ptr instead or ptr->next = nptr->next; delete nptr; return true; As far as protecting against inserting duplicates in a linked list, just parse through each element with a for loop before looking for a place to insert it.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.