class List {
private:

  class Node {
  public:
    int data;
    Node * next;
    Node (int data, Node *next) {
      Node::data = data; Node::next = next;
    }
  };

  Node *head;

  // private copy method used by copy constructor and operator=
  void copy (const List &otherList);

  // private deleteAll method used by destructor and operator=
  void deleteAll();

  // returns the sum of the values of the sublist
  int subSumValues(Node *subHead) const;

  // returns the number of values in the sublist
  int subNumValues(Node *subHead) const;

  // returns true if the values of the sublist are sorted
  // in ascending order, false otherwise
  bool subIsSortedAscending(Node *subHead);

public:

  // default contstructor: creates empty list
  List () { head = NULL; };

  // copy constructor
  List (const List &otherList);

  // destructor: destroys list
  ~List ();

  // outputs list contents to cout
  void outputList () const;

  // adds a value at the beginning of the list
  void insert (int value);

  // assigns one linked list to another
  List& operator= (const List &otherList);

  // returns the sum of the values of the list
  int sumValues() const;

  // returns the number of values in the list
  int numValues() const;

  // returns true if the values of the list are sorted
  // in ascending order, false otherwise
  bool isSortedAscending();

};