foo.cc: In function 'int main()':
foo.cc:9:7: error: no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'int')
   cin >> 7;
   ~~~~^~~~
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: 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 >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: 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 >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: invalid conversion from 'int' to 'std::ios_base& (*)(std::ios_base&)' [-fpermissive]
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'bool&' to an rvalue of type 'bool'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'short int&' to an rvalue of type 'short int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'short unsigned int&' to an rvalue of type 'short unsigned int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'int&' to an rvalue of type 'int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'unsigned int&' to an rvalue of type 'unsigned int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'long int&' to an rvalue of type 'long int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'long unsigned int&' to an rvalue of type 'long unsigned int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from 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:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'long long int&' to an rvalue of type 'long long int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(unsigned long long& __n)
       ^~~~~~~~
/usr/include/c++/7/istream:199:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'long long unsigned int&' to an rvalue of type 'long long unsigned int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(float& __f)
       ^~~~~~~~
/usr/include/c++/7/istream:214:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'float&' to an rvalue of type 'float'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(double& __f)
       ^~~~~~~~
/usr/include/c++/7/istream:218:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'double&' to an rvalue of type 'double'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(long double& __f)
       ^~~~~~~~
/usr/include/c++/7/istream:222:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: cannot bind non-const lvalue reference of type 'long double&' to an rvalue of type 'long double'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/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>] <near match>
       operator>>(void*& __p)
       ^~~~~~~~
/usr/include/c++/7/istream:235:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: invalid conversion from 'int' to 'void*' [-fpermissive]
   cin >> 7;
          ^
foo.cc:9:10: error: cannot bind rvalue '7' to 'void*&'
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:259:7: note: candidate: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>] <near match>
       operator>>(__streambuf_type* __sb);
       ^~~~~~~~
/usr/include/c++/7/istream:259:7: note:   conversion of argument 1 would be ill-formed:
foo.cc:9:10: error: invalid conversion from 'int' to 'std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}' [-fpermissive]
   cin >> 7;
          ^
foo.cc:9:7: note: candidate: operator>>(int, int) <built-in>
   cin >> 7;
   ~~~~^~~~
foo.cc:9:7: note:   no known conversion for argument 1 from 'std::istream {aka std::basic_istream<char>}' to 'int'
In file included from /usr/include/c++/7/string:53:0,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from foo.cc:1:
/usr/include/c++/7/bits/basic_string.tcc:1465:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator>>(basic_istream<_CharT, _Traits>& __in,
     ^~~~~~~~
/usr/include/c++/7/bits/basic_string.tcc:1465:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   mismatched types 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' and 'int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/istream:991:0,
                 from /usr/include/c++/7/iostream:40,
                 from foo.cc:1:
/usr/include/c++/7/bits/istream.tcc:963:5: note: candidate: template<class _CharT2, class _Traits2> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT2*)
     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
     ^~~~~~~~
/usr/include/c++/7/bits/istream.tcc:963:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   mismatched types '_CharT2*' and 'int'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/istream:991:0,
                 from /usr/include/c++/7/iostream:40,
                 from foo.cc:1:
/usr/include/c++/7/bits/istream.tcc:931:5: note: candidate: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&)
     operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
     ^~~~~~~~
/usr/include/c++/7/bits/istream.tcc:931:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   deduced conflicting types for parameter '_CharT' ('char' and 'int')
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:756:5: note: candidate: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&)
     operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
     ^~~~~~~~
/usr/include/c++/7/istream:756:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   cannot convert '7' (type 'int') to type 'unsigned char&'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:761:5: note: candidate: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&)
     operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
     ^~~~~~~~
/usr/include/c++/7/istream:761:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   cannot convert '7' (type 'int') to type 'signed char&'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:803:5: note: candidate: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*)
     operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
     ^~~~~~~~
/usr/include/c++/7/istream:803:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   cannot convert '7' (type 'int') to type 'unsigned char*'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:808:5: note: candidate: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*)
     operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
     ^~~~~~~~
/usr/include/c++/7/istream:808:5: note:   template argument deduction/substitution failed:
foo.cc:9:10: note:   cannot convert '7' (type 'int') to type 'signed char*'
   cin >> 7;
          ^
In file included from /usr/include/c++/7/iostream:40:0,
                 from foo.cc:1:
/usr/include/c++/7/istream:980:5: note: candidate: template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&)
     operator>>(_Istream&& __is, _Tp&& __x)
     ^~~~~~~~
/usr/include/c++/7/istream:980:5: note:   template argument deduction/substitution failed:
/usr/include/c++/7/istream: In substitution of 'template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_istream<char>&; _Tp = int]':
foo.cc:9:10:   required from here
/usr/include/c++/7/istream:980:5: error: no type named 'type' in 'struct std::enable_if<false, std::basic_istream<char>&>'