/in/foo.cc: In function 'int main()':
/in/foo.cc:5:2: error: 'string' was not declared in this scope
  string ans=n%3==0&&n%5==0?"YES":"NO";
  ^~~~~~
/in/foo.cc:5:2: 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:6:13: error: 'ans' was not declared in this scope
  std::cout<<ans;
             ^~~