Language: C++

#include<bits/stdc++.h>
using namespace std;

int main(){
  string s;
  cin >> s;
  vector<char> ans();
  for(int i  = 0; i < s.size(); i++){
    if(s.at(i) == '0'){
      s.push_back('0');
    }
    else if(s.at(i) == '1'){
      s.push_back('1');
    }
    else{
      if(!s.empty()) s.pop_back();
    }
  }
  for(char c : &s){
    cout << c;
  }
  cout << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:7:19: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
    7 |   vector<char> ans();
      |                   ^~
a.cc:19:17: error: no matching function for call to 'begin(std::__cxx11::basic_string<char>*&)'
   19 |   for(char c : &s){
      |                 ^
In file included from /usr/include/c++/14/bits/algorithmfwd.h:39,
                 from /usr/include/c++/14/bits/stl_algo.h:59,
                 from /usr/include/c++/14/algorithm:61,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/initializer_list:88:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'std::initializer_list<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/range_access.h:52:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&) [with _Container = std::__cxx11::basic_string<char>*]':
a.cc:19:17:   required from here
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/bits/range_access.h:52:50: error: request for member 'begin' in '__cont', which is of pointer type 'std::__cxx11::basic_string<char>*' (maybe you meant to use '->' ?)
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |                                           ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&) [with _Container = std::__cxx11::basic_string<char>*]':
a.cc:19:17:   required from here
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/bits/range_access.h:63:56: error: request for member 'begin' in '__cont', which is of pointer type 'std::__cxx11::basic_string<char>* const' (maybe you meant to use '->' ?)
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |                                                 ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types '_Tp [_Nm]' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/valarray:1227:5: note: candidate: 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'std::valarray<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/valarray:1238:5: note: candidate: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1238:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'const std::valarray<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
a.cc:19:17: error: no matching function for call to 'end(std::__cxx11::basic_string<char>*&)'
/usr/include/c++/14/initializer_list:99:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::end(initializer_list<_Tp>)'
   99 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
/usr/include/c++/14/initializer_list:99:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'std::initializer_list<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/bits/range_access.h:74:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&)'
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:74:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&) [with _Container = std::__cxx11::basic_string<char>*]':
a.cc:19:17:   required from here
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/bits/range_access.h:74:48: error: request for member 'end' in '__cont', which is of pointer type 'std::__cxx11::basic_string<char>*' (maybe you meant to use '->' ?)
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |                                         ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:85:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&)'
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:85:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&) [with _Container = std::__cxx11::basic_string<char>*]':
a.cc:19:17:   required from here
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/bits/range_access.h:85:54: error: request for member 'end' in '__cont', which is of pointer type 'std::__cxx11::basic_string<char>* const' (maybe you meant to use '->' ?)
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |                                               ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:106:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::end(_Tp (&)[_Nm])'
  106 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/usr/include/c++/14/bits/range_access.h:106:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types '_Tp [_Nm]' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/valarray:1249:5: note: candidate: 'template<class _Tp> _Tp* std::end(valarray<_Tp>&)'
 1249 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1249:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'std::valarray<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^
/usr/include/c++/14/valarray:1265:5: note: candidate: 'template<class _Tp> const _Tp* std::end(const valarray<_Tp>&)'
 1265 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1265:5: note:   template argument deduction/substitution failed:
a.cc:19:17: note:   mismatched types 'const std::valarray<_Tp>' and 'std::__cxx11::basic_string<char>*'
   19 |   for(char c : &s){
      |                 ^