/in/foo.cc: In function 'int main()':
/in/foo.cc:5:2: error: 'cin' was not declared in this scope
  cin.getline(c, 101);
  ^~~
/in/foo.cc:5:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:6:2: error: 'string' was not declared in this scope
  string s(c);
  ^~~~~~
/in/foo.cc:6:2: note: suggested alternatives:
In file included from /usr/include/c++/6/iosfwd:39:0,
                 from /usr/include/c++/6/ios:38,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stringfwd.h:74:33: note:   'std::__cxx11::string'
   typedef basic_string<char>    string;
                                 ^~~~~~
/usr/include/c++/6/bits/stringfwd.h:74:33: note:   'std::__cxx11::string'
/in/foo.cc:8:19: error: 's' was not declared in this scope
  for(int i=0; i < s.size(); ++i){
                   ^
/in/foo.cc:11:2: error: 'cout' was not declared in this scope
  cout << res;
  ^~~~
/in/foo.cc:11:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~