Language: C++

#include<bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
#define rep(i, n) for(int i = 0; i < (n); i++)

int int_len(int n) {
  int s=0;
  while(n!=0) s++, n/=10;
  return s;
}

int int_sum(int n) {
  int m=0,s=0,a=n;
  while(a!=0) s++, a/=10;
  for(int i=s-1;i>=0;i--) m+=n/((int)pow(10,i))-(n/((int)pow(10,i+1)))*10;
  return m;
}






int gcd(int a,int b)
{
 
  int r, tmp;
 
  
 
  /* 自然数 a > b を確認・入替 */
  if(a<b){
    tmp = a;
    a = b;
    b = tmp;
  }
 
  /* ユークリッドの互除法 */
  r = a % b;
  while(r!=0){
    a = b;
    b = r;
    r = a % b;
  }
 
 
 
  return b;
}







int fac(int n){
  int m=1;
  while(n>=1) m*=n,n--;
  return m;
}

int vec_sum(vector<int> v){
  int n=0;
  for(int i=0;i<v.size();i++) n+=v[i];
  return n;
}
///////////////////////////
int main() {
  string a,b,c,cnt;
  bool flaga=false;
  bool flagb=false;
  bool flagc=false;
  char ans;
  cin>>a>>b>>c;
  reverse(a.begin(),a.end());
  reverse(b.begin(),b.end());
  reverse(c.begin(),c.end());
  cnt=a[a.size()-1];
  while(true){
    if(cnt=='a' && flaga){
      ans='a';
      break;
    }else if(cnt=='a'){
      cnt=a[a.size()-1];
      a.pop_back();
    }
    if(cnt=='b' && flagb){
      ans='b';
      break;
    }else if(cnt=='b'){
      cnt=b[b.size()-1];
      b.pop_back();
    }
    if(cnt=='c' && flagc){
      ans='c';
      break;
    }else if(cnt=='c'){
      cnt=c[c.size()-1];
      c.pop_back();
    }
    if(a.size()==0){
      flaga=true;
    }
    if(b.size()==0){
      flagb=true;
    }
    if(c.size()==0){
      flagc=true;
    }
  }
  cout<<ans<<endl;
  
}
///////////////////////////



Compiler output:
a.cc: In function 'int main()':
a.cc:81:11: error: no match for 'operator==' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'char')
   81 |     if(cnt=='a' && flaga){
      |        ~~~^~~~~
      |        |    |
      |        |    char
      |        std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1103:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1103 |     operator==(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1103:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1199:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1199 |     operator==(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1199:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1274:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1274 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1274:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1366:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1366 |     operator==(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1366:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1441:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1441 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1441:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1534:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1534 |     operator==(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1534:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:1613:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1613 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1613:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/regex.h:2186:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator==(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2186 |     operator==(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2186:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::pair<_T1, _T2>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
In file included from /usr/include/c++/14/bits/char_traits.h:42,
                 from /usr/include/c++/14/string:42,
                 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/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::fpos<_StateT>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::allocator<_CharT>'
   81 |     if(cnt=='a' && flaga){
      |             ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  629 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:629:5: note:   template argument deduction/substitution failed:
a.cc:81:13: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::basic_string_view