/in/foo.cc: In constructor 'LinkList::LinkList(int)':
/in/foo.cc:20:29: warning: passing NULL to non-pointer argument 1 of 'Node::Node(int)' [-Wconversion-null]
   Node* tail = new Node(NULL);
                             ^
/in/foo.cc:20:9: warning: unused variable 'tail' [-Wunused-variable]
   Node* tail = new Node(NULL);
         ^~~~