Language: C++

#include<bits/stdc++.h>
#include<string>
using namespace std;
string a, b;
int main(){
  cin >> a >> b;
  if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
    cout << "H" << endl;
  } else if((a = 'H' && b = 'D') || (a = 'D' && b = 'H')){
    cout << "D" << endl;
  }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:15: error: no match for 'operator&&' (operand types are 'char' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |           ~~~ ^~ ~
      |           |      |
      |           char   std::string {aka std::__cxx11::basic_string<char>}
a.cc:7:15: note: candidate: 'operator&&(bool, bool)' (built-in)
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |           ~~~~^~~~
a.cc:7:15: note:   no known conversion for argument 2 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'bool'
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166,
                 from a.cc:1:
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1206:1: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   mismatched types 'const std::valarray<_Tp>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1206:1: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   mismatched types 'const std::valarray<_Tp>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
/usr/include/c++/14/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)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1206:1: note:   template argument deduction/substitution failed:
a.cc:7:18: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::valarray<_Tp>'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                  ^
a.cc:7:37: error: no match for 'operator&&' (operand types are 'char' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                                 ~~~ ^~ ~
      |                                 |      |
      |                                 char   std::string {aka std::__cxx11::basic_string<char>}
a.cc:7:37: note: candidate: 'operator&&(bool, bool)' (built-in)
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                                 ~~~~^~~~
a.cc:7:37: note:   no known conversion for argument 2 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'bool'
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:40: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                                        ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:40: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'char'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                                        ^
/usr/include/c++/14/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)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:415:5: note:   template argument deduction/substitution failed:
a.cc:7:40: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
    7 |   if((a = 'H' && b ='H') ||(a = 'D' && b = 'D')){
      |                                        ^
/usr/include/c++/14/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