foo.cc: In function 'int main()':
foo.cc:11:34: error: no match for 'operator<<' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                               ~~~^~~~~~
      |                               |       |
      |                               |       int
      |                               std::istream {aka std::basic_istream<char>}
foo.cc:11:34: note: candidate: 'operator<<(int, int)' (built-in)
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                               ~~~^~~~~~
foo.cc:11:34: note:   no known conversion for argument 1 from 'std::istream' {aka 'std::basic_istream<char>'} to 'int'
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/string:55,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/locale_classes.h:40,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:41,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:38,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/basic_string.h:6531:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)'
 6531 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/basic_string.h:6531:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/ios_base.h:46,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ios:42,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:38,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/system_error:279:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::error_code&)'
  279 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/system_error:279:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:513:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, _CharT)'
  513 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:513:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:518:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, char)'
  518 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:518:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:524:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char)'
  524 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:524:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:530:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, signed char)'
  530 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:530:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:535:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, unsigned char)'
  535 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:535:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:594:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const _CharT*)'
  594 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:594:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:829,
                 from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/ostream.tcc:321:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*)'
  321 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/bits/ostream.tcc:321:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:611:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)'
  611 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:611:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:624:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*)'
  624 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:624:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:629:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*)'
  629 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:629:5: note:   template argument deduction/substitution failed:
foo.cc:11:39: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
   11 |         for(int i=1;i<=n;i++) cin<<a[i];
      |                                       ^
In file included from /nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/iostream:39,
                 from foo.cc:1:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:750:5: note: candidate: 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)'
  750 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:750:5: note:   template argument deduction/substitution failed:
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream: In substitution of 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_istream<char>&; _Tp = int]':
foo.cc:11:32:   required from here
/nix/store/wy4ywjsch9q2hj5lphqjdg9p2kf7w0ls-gcc-11.3.0/include/c++/11.3.0/ostream:750:5: error: no type named 'type' in 'struct std::enable_if<false, void>'

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