View Compilation Error

0_0_18564536_10214.cpp: In function 'int main()':
0_0_18564536_10214.cpp:16:2: error: incomplete type 'std::ios {aka std::basic_ios<char>}' used in nested name specifier
  ios::sync_with_stdio(false);
  ^
0_0_18564536_10214.cpp:17:9: error: 'cin' was not declared in this scope
  while (cin >> a >> b) {
         ^
0_0_18564536_10214.cpp:34:3: error: 'cout' was not declared in this scope
   cout << ans << endl;
   ^
0_0_18564536_10214.cpp:34:18: error: 'endl' was not declared in this scope
   cout << ans << endl;
                  ^