Language: C++

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)

int main(){
  string s; cin >> s;
  ll count = 0;
  rep(i,s.length()) if(s[i] == '0') count++;
  cout << max(count, s.length() - count) << endl;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:5:3: error: 'string' was not declared in this scope
    5 |   string s; cin >> s;
      |   ^~~~~~
a.cc:5:3: note: suggested alternatives:
In file included from /usr/include/c++/14/string:41,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:5:13: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    5 |   string s; cin >> s;
      |             ^~~
      |             std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:5:20: error: 's' was not declared in this scope
    5 |   string s; cin >> s;
      |                    ^
a.cc:6:3: error: 'll' was not declared in this scope
    6 |   ll count = 0;
      |   ^~
a.cc:7:37: error: 'count' was not declared in this scope; did you mean 'std::count'?
    7 |   rep(i,s.length()) if(s[i] == '0') count++;
      |                                     ^~~~~
      |                                     std::count
In file included from /usr/include/c++/14/algorithm:86,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/pstl/glue_algorithm_defs.h:101:1: note: 'std::count' declared here
  101 | count(_ExecutionPolicy&& __exec, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value);
      | ^~~~~
a.cc:8:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    8 |   cout << max(count, s.length() - count) << endl;
      |   ^~~~
      |   std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:8:15: error: 'count' was not declared in this scope; did you mean 'std::count'?
    8 |   cout << max(count, s.length() - count) << endl;
      |               ^~~~~
      |               std::count
/usr/include/c++/14/pstl/glue_algorithm_defs.h:101:1: note: 'std::count' declared here
  101 | count(_ExecutionPolicy&& __exec, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value);
      | ^~~~~
a.cc:8:11: error: 'max' was not declared in this scope; did you mean 'std::max'?
    8 |   cout << max(count, s.length() - count) << endl;
      |           ^~~
      |           std::max
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: 'std::max' declared here
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
a.cc:8:45: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    8 |   cout << max(count, s.length() - count) << endl;
      |                                             ^~~~
      |                                             std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~