/in/foo.cc: In function 'void Merge(Node*, Node*)':
/in/foo.cc:77:23: warning: left operand of comma operator has no effect [-Wunused-value]
  for(p=head1,q=head2;p!=NULL,q!=NULL;)
                       ^
/in/foo.cc: In function 'void Unique(Node*, Node*)':
/in/foo.cc:134:11: warning: unused variable 'q' [-Wunused-variable]
  Node *p,*q;
           ^