/in/foo.cc: In function 'std::vector<bool> turn(std::vector<bool>, int)':
/in/foo.cc:38:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 1; i < ans.size() - 1; i++)
                  ~~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:58:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for (int i = 0; i < 2 * n + 3; i++)  ans.push_back(0);  ans[n + 1] = 1;
  ^~~
/in/foo.cc:58:58: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  for (int i = 0; i < 2 * n + 3; i++)  ans.push_back(0);  ans[n + 1] = 1;
                                                          ^~~