---

Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:9:10: error: no match for ‘operator>>’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘int’)
     cout >> a*x+b*y;
     ~~~~~^~~~~~~~~~
Main.cc:9:10: note: candidate: operator>>(int, int) 
Main.cc:9:10: note:   no known conversion for argument 1 from ‘std::ostream {aka std::basic_ostream}’ 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 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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream<_CharT, _Traits>’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’
     cout >> a*x+b*y;
                   ^
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:9:19: note:   ‘std::ostream {aka std::basic_ostream}’ is not derived from ‘std::basic_istream’
     cout >> a*x+b*y;
                   ^
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:
/usr/include/c++/7/istream: In substitution of ‘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&&) [with _Istream = std::basic_ostream&; _Tp = int]’:
Main.cc:9:19:   required from here
/usr/include/c++/7/istream:980:5: error: no type named ‘type’ in ‘struct std::enable_if’
Main.cc:9:16: warning: suggest parentheses around ‘+’ inside ‘>>’ [-Wparentheses]
     cout >> a*x+b*y;
             ~~~^~~~