/in/foo.cc: In function 'int main()':
/in/foo.cc:8:14: error: no match for 'operator=' (operand types are 'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' and 'int')
     cin>>len=3;
              ^
In file included from /usr/include/c++/6/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/istream:625:7: note: candidate: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator=(std::basic_istream<_CharT, _Traits>&&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator=(basic_istream&& __rhs)
       ^~~~~~~~
/usr/include/c++/6/istream:625:7: note:   no known conversion for argument 1 from 'int' to 'std::basic_istream<char>&&'