/in/foo.cc: In function 'void unique(node*)':
/in/foo.cc:71:22: warning: variable 'pre2' set but not used [-Wunused-but-set-variable]
  node* pre = NULL, * pre2 = NULL, * i, * j;
                      ^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:145:18: warning: unused variable 'i' [-Wunused-variable]
  int n1, n2, n3, i, t;
                  ^
/in/foo.cc:145:21: warning: unused variable 't' [-Wunused-variable]
  int n1, n2, n3, i, t;
                     ^