/in/foo.cc: In function 'int main()':
/in/foo.cc:7:7: error: no match for 'operator<=' (operand types are 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' and 'int')
   if(a<=0&&a>=59.5)cout<<"不及格";
      ~^~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_pair.h:460:5: note: candidate: template<class _T1, class _T2> constexpr bool std::operator<=(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
     operator<=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
     ^~~~~~~~
/usr/include/c++/6/bits/stl_pair.h:460:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::pair<_T1, _T2>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:316:5: note: candidate: template<class _Iterator> bool std::operator<=(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
     operator<=(const reverse_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:316:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::reverse_iterator<_Iterator>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:373:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<=(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator<=(const reverse_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:373:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::reverse_iterator<_Iterator>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:1149:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<=(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)
     operator<=(const move_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1149:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::move_iterator<_IteratorL>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:1155:5: note: candidate: template<class _Iterator> bool std::operator<=(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)
     operator<=(const move_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1155:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   'std::__cxx11::string {aka std::__cxx11::basic_string<char>}' is not derived from 'const std::move_iterator<_IteratorL>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/basic_string.h:5226:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5226:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' and 'int'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/basic_string.h:5239:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
     operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5239:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   mismatched types 'const _CharT*' and 'int'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/string:52:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/basic_string.h:5251:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<=(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)
     operator<=(const _CharT* __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/basic_string.h:5251:5: note:   template argument deduction/substitution failed:
/in/foo.cc:7:9: note:   mismatched types 'const _CharT*' and 'std::__cxx11::basic_string<char>'
   if(a<=0&&a>=59.5)cout<<"不及格";
         ^
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:920:5: note: candidate: template<class _Iterator, class _Container> bool __gnu_cxx::operator<=(const __gnu_cxx::__normal_iterator<_Iterator, _Container>&, const __gnu_cxx::__normal_iterator<_Iterator, _Container>&)
     operator<=(const __normal_iterator<_Iterator, _Container>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:920:5: note:   template argument deduction/substitution failed:
/in/foo.cc