Language: C++

#include<bits/stdc++.h>
using  std;
int main()
{
  int i,k,n,m;
  string s;
  cin >> n >> s;
  vector<int> white(n+1);
  vector<int> black(n+1);
  white.at(0)=0;
  black.at(0)=0;
  for(i=0;i<n;i++)
  {
    if(s.at(i)=='#')
    { white.at(i+1)=white.at(i)+1;
    }
    else
    {
      white.at(i+1)=white.at(i);
    }
  }
 for(i=0;i<n;i++)
  {
    if(s.at(n-1-i)=='.')
    {  black.at(i+1)=black.at(i)+1;
    }
   else
    {
      black.at(i+1)=black.at(i);
    }
  } 
  m=1000000;
  for(i=0;i<n+1;i++)
  {
    if(m>=white.at(i)+black.at(n-i))
      m=white.at(i)+black.at(n-i);
  //  cout << m << endl;
  }
  cout << m << endl;
}

Compiler output:
a.cc:2:8: error: expected nested-name-specifier before 'std'
    2 | using  std;
      |        ^~~
a.cc: In function 'int main()':
a.cc:6:3: error: 'string' was not declared in this scope
    6 |   string s;
      |   ^~~~~~
a.cc:6:3: 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:7:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |   cin >> n >> 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:7:15: error: 's' was not declared in this scope
    7 |   cin >> n >> s;
      |               ^
a.cc:8:3: error: 'vector' was not declared in this scope
    8 |   vector<int> white(n+1);
      |   ^~~~~~
a.cc:8:3: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53:
/usr/include/c++/14/bits/stl_vector.h:428:11: note:   'std::vector'
  428 |     class vector : protected _Vector_base<_Tp, _Alloc>
      |           ^~~~~~
/usr/include/c++/14/vector:93:13: note:   'std::pmr::vector'
   93 |       using vector = std::vector<_Tp, polymorphic_allocator<_Tp>>;
      |             ^~~~~~
a.cc:8:10: error: expected primary-expression before 'int'
    8 |   vector<int> white(n+1);
      |          ^~~
a.cc:9:10: error: expected primary-expression before 'int'
    9 |   vector<int> black(n+1);
      |          ^~~
a.cc:10:3: error: 'white' was not declared in this scope; did you mean 'write'?
   10 |   white.at(0)=0;
      |   ^~~~~
      |   write
a.cc:11:3: error: 'black' was not declared in this scope
   11 |   black.at(0)=0;
      |   ^~~~~
a.cc:39:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   39 |   cout << m << 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:39:16: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   39 |   cout << m << 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)
      |     ^~~~