Main.cc: In function ‘int main()’: Main.cc:21:8: error: no match for ‘operator>>’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘’) cout>>endl; ~~~~^~~~~~ 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 Main.cc:1: /usr/include/c++/7/bits/basic_string.tcc:1465:5: note: candidate: template 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: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/istream:991:0, from /usr/include/c++/7/iostream:40, from Main.cc:1: /usr/include/c++/7/bits/istream.tcc:963:5: note: candidate: template 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: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/istream:991:0, from /usr/include/c++/7/iostream:40, from Main.cc:1: /usr/include/c++/7/bits/istream.tcc:931:5: note: candidate: template 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: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/iostream:40:0, from Main.cc:1: /usr/include/c++/7/istream:756:5: note: candidate: template std::basic_istream& std::operator>>(std::basic_istream&, unsigned char&) operator>>(basic_istream& __in, unsigned char& __c) ^~~~~~~~ /usr/include/c++/7/istream:756:5: note: template argument deduction/substitution failed: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/iostream:40:0, from Main.cc:1: /usr/include/c++/7/istream:761:5: note: candidate: template std::basic_istream& std::operator>>(std::basic_istream&, signed char&) operator>>(basic_istream& __in, signed char& __c) ^~~~~~~~ /usr/include/c++/7/istream:761:5: note: template argument deduction/substitution failed: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/iostream:40:0, from Main.cc:1: /usr/include/c++/7/istream:803:5: note: candidate: template std::basic_istream& std::operator>>(std::basic_istream&, unsigned char*) operator>>(basic_istream& __in, unsigned char* __s) ^~~~~~~~ /usr/include/c++/7/istream:803:5: note: template argument deduction/substitution failed: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/iostream:40:0, from Main.cc:1: /usr/include/c++/7/istream:808:5: note: candidate: template std::basic_istream& std::operator>>(std::basic_istream&, signed char*) operator>>(basic_istream& __in, signed char* __s) ^~~~~~~~ /usr/include/c++/7/istream:808:5: note: template argument deduction/substitution failed: Main.cc:21:10: note: ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’ cout>>endl; ^~~~ In file included from /usr/include/c++/7/iostream:40:0, from Main.cc:1: /usr/include/c++/7/istream:980:5: note: candidate: template typename std::enable_if >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable::__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: Main.cc:21:10: note: couldn't deduce template parameter ‘_Tp’ cout>>endl; ^~~~