foo.cc: In function 'void add(int, int, int)':
foo.cc:17:7: error: invalid types 'int[int]' for array subscript
  t[now] = t;
       ^
foo.cc: In function 'int main()':
foo.cc:25:2: error: 'cin' was not declared in this scope
  cin >> n >> s;
  ^~~
foo.cc:25:2: note: suggested alternative:
In file included from foo.cc:1:0:
/usr/include/c++/7/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。