/in/foo.cc: In function 'int main()':
/in/foo.cc:21:6: error: no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'node')
   cin>>a[i];
   ~~~^~~~~~
In file included from /usr/include/c++/6/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/istream:120:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(__istream_type& (*__pf)(__istream_type&))
       ^~~~~~~~
/usr/include/c++/6/istream:120:7: note:   no known conversion for argument 1 from 'node' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}'
/usr/include/c++/6/istream:124:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
       operator>>(__ios_type& (*__pf)(__ios_type&))
       ^~~~~~~~
/usr/include/c++/6/istream:124:7: note:   no known conversion for argument 1 from 'node' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}'
/usr/include/c++/6/istream:131:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(ios_base& (*__pf)(ios_base&))
       ^~~~~~~~
/usr/include/c++/6/istream:131:7: note:   no known conversion for argument 1 from 'node' to 'std::ios_base& (*)(std::ios_base&)'
/usr/include/c++/6/istream:168:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(bool& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:168:7: note:   no known conversion for argument 1 from 'node' to 'bool&'
/usr/include/c++/6/istream:172:7: note: candidate: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator>>(short& __n);
       ^~~~~~~~
/usr/include/c++/6/istream:172:7: note:   no known conversion for argument 1 from 'node' to 'short int&'
/usr/include/c++/6/istream:175:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(unsigned short& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:175:7: note:   no known conversion for argument 1 from 'node' to 'short unsigned int&'
/usr/include/c++/6/istream:179:7: note: candidate: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator>>(int& __n);
       ^~~~~~~~
/usr/include/c++/6/istream:179:7: note:   no known conversion for argument 1 from 'node' to 'int&'
/usr/include/c++/6/istream:182:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(unsigned int& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:182:7: note:   no known conversion for argument 1 from 'node' to 'unsigned int&'
/usr/include/c++/6/istream:186:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(long& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:186:7: note:   no known conversion for argument 1 from 'node' to 'long int&'
/usr/include/c++/6/istream:190:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(unsigned long& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:190:7: note:   no known conversion for argument 1 from 'node' to 'long unsigned int&'
/usr/include/c++/6/istream:195:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(long long& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:195:7: note:   no known conversion for argument 1 from 'node' to 'long long int&'
/usr/include/c++/6/istream:199:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(unsigned long long& __n)
       ^~~~~~~~
/usr/include/c++/6/istream:199:7: note:   no known conversion for argument 1 from 'node' to 'long long unsigned int&'
/usr/include/c++/6/istream:214:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(float& __f)
       ^~~~~~~~
/usr/include/c++/6/istream:214:7: note:   no known conversion for argument 1 from 'node' to 'float&'
/usr/include/c++/6/istream:218:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(double& __f)
       ^~~~~~~~
/usr/include/c++/6/istream:218:7: note:   no known conversion for argument 1 from 'node' to 'double&'
/usr/include/c++/6/istream:222:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(long double& __f)
       ^~~~~~~~
/usr/include/c++/6/istream:222:7: note:   no known conversion for argument 1 from 'node' to 'long double&'
/usr/include/c++/6/istream:235:7: note: candidate: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]
       operator>>(void*& __p)
       ^~~~~~~~
/usr/include/c++/6/istream:235:7: note:   no known conversion for argument 1 from 'node' to 'void*&'
/usr/include/c++/6/istream:259:7: note: candidate: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::_