View Compilation Error

0_0_15198441_5008.cpp: In function 'int main()':
0_0_15198441_5008.cpp:38:2: error: incomplete type 'std::ios {aka std::basic_ios<char>}' used in nested name specifier
  ios::sync_with_stdio(false);
  ^
0_0_15198441_5008.cpp:39:2: error: 'cin' was not declared in this scope
  cin >> tst_case;
  ^
0_0_15198441_5008.cpp:44:3: error: 'cout' was not declared in this scope
   cout << setiosflags(ios::fixed) << setprecision(3) << ans << endl;
   ^
0_0_15198441_5008.cpp:44:23: error: incomplete type 'std::ios {aka std::basic_ios<char>}' used in nested name specifier
   cout << setiosflags(ios::fixed) << setprecision(3) << ans << endl;
                       ^
0_0_15198441_5008.cpp:44:64: error: 'endl' was not declared in this scope
   cout << setiosflags(ios::fixed) << setprecision(3) << ans << endl;
                                                                ^