More default parameters

Node::Node(int  val = 0,  Node  *next
    = NULL)  :  number(val),  next(next)  {  }
Can use as
     head  =  new  Node(o.head->number,
                                       o.head->next);
     head  =  new  Node(o.head->number,
                                       NULL);
     head  =  new  Node(o.head->number);
     head  =  new  Node();
This is also the default constructor