I am trying to add three functions to this code so that I can add an entire list at one time to another list instead of having to add individual elements one at a time. Here is what I have so far but it is not working.

#ifndef LINKEDLIST_H
#define LINKEDLIST_H
#include <stdexcept>
using namespace std;

template<typename T>
class Node
{
public:
  T element;  // Element contained in the node
  Node<T> *next; // Pointer to the next node

  Node() // No-arg constructor
  {
    next = NULL;
  }

  Node(T element) // Constructor
  {
    this->element = element;
    next = NULL;
  }
};

template<typename T>
class Iterator : public std::iterator<std::forward_iterator_tag, T>
{
public:
  Iterator(Node<T> *p)
  {
    current = p;
  };

  Iterator operator++()
  {
    current = current -> next;
    return *this;
  }

  T & operator*()
  {
    return current -> element;
  }

  bool operator==(const Iterator<T> &iterator)
  {
    return current == iterator.current;
  }

  bool operator!=(const Iterator<T> &iterator)
  {
    return current != iterator.current;
  }

private:
  Node<T> *current;
};

template<typename T>
class LinkedList
{
public:
  LinkedList();
  LinkedList(LinkedList<T> &list);
  virtual ~LinkedList();
  void addFirst(T element);
  void addLast(T element);
  T getFirst() const;
  T getLast() const;
  T removeFirst() throw (runtime_error);
  T removeLast();
  void add(T element);
  void add(int index, T element);
  void clear();
  bool contains(T element) const;
  T get(int index) const;
  int indexOf(T element) const;
  bool isEmpty() const;
  int lastIndexOf(T element) const;
  void remove(T element);
  int getSize() const;
  T removeAt(int index);
  T set(int index, T element);
  void addAll(LinkedList<T> &otherList) const;
  void removeAll(const LinkedList<T> &otherList);
  void retainAll(const LinkedList<T> &otherList); 

  Iterator < T > begin()
  {
    return Iterator < T > (head);
  };

  Iterator < T > end()
  {
    return Iterator < T > (tail->next);
  };

private:
  Node<T> *head, *tail;
  int size;
};

template<typename T>
LinkedList<T>::LinkedList()
{
  head = tail = NULL;
  size = 0;
}

template<typename T>
LinkedList<T>::LinkedList(LinkedList<T> &list)
{
  head = tail = NULL;
  size = 0;

  Node<T> *current = list.head;
  while (current != NULL)
  {
    this->add(current->element);
    current = current->next;
  }
}

template<typename T>
LinkedList<T>::~LinkedList()
{
  clear();
}

template<typename T>
void LinkedList<T>::addFirst(T element)
{
  Node<T> *newNode = new Node<T>(element);
  newNode->next = head;
  head = newNode;
  size++;

  if (tail == NULL)
    tail = head;
}

template<typename T>
void LinkedList<T>::addLast(T element)
{
  if (tail == NULL)
  {
    head = tail = new Node<T>(element);
  }
  else
  {
    tail->next = new Node<T>(element);
    tail = tail->next;
  }

  size++;
}

template<typename T>
T LinkedList<T>::getFirst() const
{
  if (size == 0)
    throw runtime_error("Index out of range");
  else
    return head->element;
}

template<typename T>
T LinkedList<T>::getLast() const
{
  if (size == 0)
    throw runtime_error("Index out of range");
  else
    return tail->element;
}

template<typename T>
T LinkedList<T>::removeFirst() throw (runtime_error)
{
  if (size == 0)
   throw runtime_error("No elements in the list");
  else
  {
    Node<T> *temp = head;
    head = head->next;
    if (head == NULL) tail = NULL;
    size--;
    T element = temp->element;
    delete temp;
    return element;
  }
}

template<typename T>
T LinkedList<T>::removeLast()
{
  if (size == 0)
    throw runtime_error("No elements in the list");
  else if (size == 1)
  {
    Node<T> *temp = head;
    head = tail = NULL;
    size = 0;
    T element = temp->element;
    delete temp;
    return element;
  }
  else
  {
    Node<T> *current = head;

    for (int i = 0; i < size - 2; i++)
      current = current->next;

    Node<T> *temp = tail;
    tail = current;
    tail->next = NULL;
    size--;
    T element = temp->element;
    delete temp;
    return element;
  }
}

template<typename T>
void LinkedList<T>::add(T element)
{
  addLast(element);
}

template<typename T>
void LinkedList<T>::add(int index, T element)
{
  if (index == 0)
    addFirst(element);
  else if (index >= size)
    addLast(element);
  else
  {
    Node<T> *current = head;
    for (int i = 1; i < index; i++)
      current = current->next;
    Node<T> *temp = current->next;
    current->next = new Node<T>(element);
    (current->next)->next = temp;
    size++;
  }
}

template<typename T>
void LinkedList<T>::clear()
{
  while (head != NULL)
  {
    Node<T> *temp = head;
    head = head->next;
    delete temp;
  }

  tail = NULL;
}

template<typename T>
T LinkedList<T>::get(int index) const
{
  if (index < 0 || index > size - 1)
    throw runtime_error("Index out of range");

  Node<T> *current = head;
  for (int i = 0; i < index; i++)
    current = current->next;

  return current->element;
}

template<typename T>
int LinkedList<T>::indexOf(T element) const
{
  // Implement it in this exercise
  Node<T> *current = head;
  for (int i = 0; i < size; i++)
  {
    if (current->element == element)
      return i;
    current = current->next;
  }

  return -1;
}

template<typename T>
bool LinkedList<T>::isEmpty() const
{
  return head == NULL;
}

template<typename T>
int LinkedList<T>::getSize() const
{
  return size;
}

template<typename T>
T LinkedList<T>::removeAt(int index)
{
  if (index < 0 || index >= size)
    throw runtime_error("Index out of range");
  else if (index == 0)
    return removeFirst();
  else if (index == size - 1)
    return removeLast();
  else
  {
    Node<T> *previous = head;

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

    Node<T> *current = previous->next;
    previous->next = current->next;
    size--;
    T element = current->element;
    delete current;
    return element;
  }
}
//Add all elements in otherList to this list
template<typename T>
void LinkedList<T>::addAll(LinkedList<T> &otherList) const
{
	addLast(otherList.head);
	otherList.removeFirst();
	size++;
}
//Remove all elements from otherList from this list
template<typename T>
void LinkedList<T>::removeAll(const LinkedList<T> &otherList)
{
}
//Retain the elements in this list if they are also in otherList
template<typename T>
void LinkedList<T>::retainAll(const LinkedList<T> &otherList)
{
}

#endif

The function that is not working is the addAll function.

The function that is not working is the addAll Function. When I try to compile it I get an error that reads cannot convert 'this' pointer from LinkedList<T> const to LinkedList<T> & I am not really sure what that means.

I apologize, there should be quotations before cannot convert and after the &
:)

Your addAll function is declared 'const', but inside the function you call 'addLast' which is not declared const.

That is where it tries to convert the 'this' pointer(itself) from a const ...&(because addAll is const) to a ...&.

That's not possible.

Do you understand the concept of declaring a function 'const'?

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