Language: C++

#include <iostream>

int main(){
  int x;
  cin >> c;
  if (x >= 400 && x < 599){
    cout << 8 << endl;
    }
  else if (x >= 600 && x < 799){
    cout << 7 << endl;
  }
  else if (x >= 800 && x < 999){
    cout << 6 << endl;
  }
  else if (x <= 1000 && x < 1199){
    cout << 5 << endl;
  }
  else if (x >= 1200 && x < 1399){
    cout << 4 << end;
  }
  else if (x >= 1400 && x < 1599){
    cout << 3 << endl;
  }
  else if (x >= 1600 && x < 1799){
    cout << 2 << endl;
  }
  else if (x >= 1800 && x < 1999){
    cout << 1 << endl;
  }

}

Compiler output:
a.cc: In function 'int main()':
a.cc:5:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    5 |   cin >> c;
      |   ^~~
      |   std::cin
In file included from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:5:10: error: 'c' was not declared in this scope
    5 |   cin >> c;
      |          ^
a.cc:7:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    7 |     cout << 8 << 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:7:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    7 |     cout << 8 << endl;
      |                  ^~~~
      |                  std::endl
In file included from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:10:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |     cout << 7 << 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:10:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |     cout << 7 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:13:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   13 |     cout << 6 << 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:13:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   13 |     cout << 6 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:16:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |     cout << 5 << 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:16:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   16 |     cout << 5 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:19:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   19 |     cout << 4 << end;
      |     ^~~~
      |     std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:19:18: error: 'end' was not declared in this scope; did you mean 'std::end'?
   19 |     cout << 4 << end;
      |                  ^~~
      |                  std::end
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40:
/usr/include/c++/14/bits/range_access.h:116:37: note: 'std::end' declared here
  116 |   template<typename _Tp> const _Tp* end(const valarray<_Tp>&) noexcept;
      |                                     ^~~
a.cc:22:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   22 |     cout << 3 << 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:22:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   22 |     cout << 3 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:25:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   25 |     cout << 2 << 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:25:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   25 |     cout << 2 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:28:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   28 |     cout << 1 << 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:28:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   28 |     cout << 1 << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~