/in/foo.cc: In function 'int main()':
/in/foo.cc:5:5: error: no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'int')
  cin>>41;
  ~~~^~~~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(__istream_type& (*__pf)(__istream_type&))
       ^~~~~~~~
/usr/include/c++/7/istream:120:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: invalid conversion from 'int' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}' [-fpermissive]
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(__ios_type& (*__pf)(__ios_type&))
       ^~~~~~~~
/usr/include/c++/7/istream:124:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: invalid conversion from 'int' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}' [-fpermissive]
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(ios_base& (*__pf)(ios_base&))
       ^~~~~~~~
/usr/include/c++/7/istream:131:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: invalid conversion from 'int' to 'std::ios_base& (*)(std::ios_base&)' [-fpermissive]
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(bool& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:168:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'bool&' to an rvalue of type 'bool'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(short& __n);
       ^~~~~~~~
/usr/include/c++/7/istream:172:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'short int&' to an rvalue of type 'short int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(unsigned short& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:175:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'short unsigned int&' to an rvalue of type 'short unsigned int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(int& __n);
       ^~~~~~~~
/usr/include/c++/7/istream:179:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'int&' to an rvalue of type 'int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(unsigned int& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:182:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'unsigned int&' to an rvalue of type 'unsigned int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(long& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:186:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'long int&' to an rvalue of type 'long int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(unsigned long& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:190:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'long unsigned int&' to an rvalue of type 'long unsigned int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(long long& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:195:7: note:   conversion of argument 1 would be ill-formed:
/in/foo.cc:5:7: error: cannot bind non-const lvalue reference of type 'long long int&' to an rvalue of type 'long long int'
  cin>>41;
       ^~
In file included from /usr/include/c++/7/iostream:40:0,
                 from /in/foo.cc:1:
/usr/include/c++/7/istream:199:7: note: candidate: std::b