I'm trying to add a node to the beginning of a linked list. Here is my code for it, but when I run tests on it, it doesn't work. Any ideas on what I might be doing incorrectly? Thanks in advance for your help!
void List<T>::insertFront(T const & insert)
{
ListNode * newNode = new ListNode(insert);
if (head != NULL)
{
head->prev = newNode;
head = head->prev;
head->prev = NULL;
}
else
{
head = newNode;
tail = newNode;
}
}
A doubly linked list is linked 2 ways, you're only attaching the new node in one way.
You need a:
newnode->next = head;
in there before you unlink the old head.
Try this.
Below method is only taking the input and making a doubly link list
node DoublyLinkedList()
{
node *list, *tptr, *nptr;
int n, item;
cout << "Enter numbers of node: ";
cin >> n;
list = NULL;
tptr = NULL;
for (int i = 0; i < n; i++)
{
//Input new node value
cout << "Enter Item " << i + 1 << ": ";
cin >> item;
//Creating new node
nptr = new(node);
nptr->back = NULL;
nptr->data = item;
nptr->next = NULL;
if (list == NULL)
{
list = nptr;
tptr = nptr;
}
else
{
tptr->next = nptr;
nptr->back = tptr;
tptr = nptr;
}
}
cout << endl;
tptr = list;
while (tptr != NULL)
{
cout << tptr->data;
tptr = tptr->next;
if (tptr != NULL)
{
cout << "<=>";
}
}
return *list;
}
Inserting the the new node using below method
void InsertToDoubly()
{
node *list, *tptr, *nptr, *pptr;
int newItem;
list = new(node);
tptr = NULL;
pptr = NULL;
*list = DoublyLinkedList(); // See this method implementation above.
cout << endl;
cout << "Input new node value to insert: ";
cin >> newItem;
nptr = new(node);
nptr->back = NULL;
nptr->data = newItem;
nptr->next = NULL;
tptr = list;
int i = 0;
while (tptr != NULL && tptr->data < newItem)
{
pptr = tptr;
tptr = tptr->next;
i++;
}
if (i == 0)
{
// Inserting at the beggining position.
nptr->next = tptr;
tptr->back = nptr;
list = nptr;
}
else if (tptr == NULL)
{
//Inserting at the last position
pptr->next = nptr;
nptr->back = pptr;
}
else
{
//Inserting into the middle position
pptr->next = nptr;
nptr->back = pptr;
nptr->next = tptr;
tptr->back = nptr;
}
tptr = list;
ShowNode(tptr);
cout << endl;
}
Main method
int main()
{
InsertToDoubly();
}
