foo.cc: In function ‘int main()’:
foo.cc:13:32: error: no match for ‘operator&&’ (operand types are ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} and ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’})
   13 |                         if(a[i]&&a[j])
      |                            ~~~~^~~~~~
      |                               |     |
      |                               |     basic_string<[...]>
      |                               basic_string<[...]>
foo.cc:13:32: note: candidate: ‘operator&&(bool, bool)’ (built-in)
   13 |                         if(a[i]&&a[j])
      |                            ~~~~^~~~~~
foo.cc:13:32: note:   no known conversion for argument 2 from ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} to ‘bool’
In file included from /nix/gcc-13.3.0/include/c++/13.3.0/valarray:605,
                 from stdc++.h:166:
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note: candidate: ‘template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__logical_and, typename _Dom1::value_type>::result_type> std::operator&&(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(&&, struct std::__logical_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__logical_and, typename _Dom1::value_type>::result_type> std::operator&&(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(&&, struct std::__logical_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__logical_and, typename _Dom1::value_type>::result_type> std::operator&&(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(&&, struct std::__logical_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__logical_and, typename _Dom1::value_type>::result_type> std::operator&&(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(&&, struct std::__logical_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__logical_and, typename _Dom1::value_type>::result_type> std::operator&&(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  415 |     _DEFINE_EXPR_BINARY_OPERATOR(&&, struct std::__logical_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__logical_and, _Tp>::result_type> std::operator&&(const valarray<_Tp>&, const valarray<_Tp>&)’
 1206 | _DEFINE_BINARY_OPERATOR(&&, __logical_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::valarray<_Tp>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__logical_and, _Tp>::result_type> std::operator&&(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)’
 1206 | _DEFINE_BINARY_OPERATOR(&&, __logical_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::valarray<_Tp>’
   13 |                         if(a[i]&&a[j])
      |                                     ^
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__logical_and, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__logical_and, _Tp>::result_type> std::operator&&(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)’
 1206 | _DEFINE_BINARY_OPERATOR(&&, __logical_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.3.0/include/c++/13.3.0/valarray:1206:1: note:   template argument deduction/substitution failed:
foo.cc:13:37: note:   ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’} is not derived from ‘const std::valarray<_Tp>’
   13 |                         if(a[i]&&a[j])
      |                                     ^