Компиляция...
p21-1.cpp
.\p21-1.cpp(8) : error C2679: бинарный '>>': не найден оператор, принимающий правый операнд типа 'main::days' (или приемлемое преобразование отсутствует)
        C:\Program Files\C++\VC\include\istream(1144): может быть 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char *)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(1146): или       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(1148): или       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char *)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(1150): или       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(155): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_istream<_Elem,_Traits> &(__cdecl *)(std::basic_istream<_Elem,_Traits> &))'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(161): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(168): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::ios_base &(__cdecl *)(std::ios_base &))'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(175): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::_Bool &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(194): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(short &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(228): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned short &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(247): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(int &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        C:\Program Files\C++\VC\include\istream(273): или       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned int &)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]