l2u1

struct List
{
  List()
  {
    first = nullptr;
  }

  void add_node(int value)
  {
    Node* _new{new Node{value}};
    first = _new;
    _new->set_next(_new);
    //https://i.kym-cdn.com/entries/icons/mobile/000/023/397/C-658VsXoAo3ovC.jpg
  }

  Node* first;
};

struct Node
{
  Node(int _value)
   :
  {
    value = _value;
    next = nullptr;
  }

  void set_next(Node* _next)
  {
    next = _next;
  }

  int value;
  Node* next;
};

int main()
{
  List l{};

  l.add_node(5);
  /**
  +-----+        +--------------------+
  |     |        |  next:     ptr========++
  |first|===++=> |--------------------|  ||
  |     |   ||   | value:    5        |  ||
  +-----+   ||   +--------------------+  ||
            =============================++

  */
}