/in/foo.cc: In function 'void unique(node*)':
/in/foo.cc:66:22: 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:104:17: warning: unused variable 'i' [-Wunused-variable]
  int n1, n2, n3,i, t;
                 ^
/in/foo.cc:104:20: warning: unused variable 't' [-Wunused-variable]
  int n1, n2, n3,i, t;
                    ^