Language: C++

#include<iostream>
#include<string>
 
int main(){
  string b;
  
  cin >> b ;
  
  if(b =='A'){
    cout<<"T"<<endl;
  }else if(b =='T'){
        cout<<"A"<<endl;
  }else if(b =='G'){
        cout<<"C"<<endl;
  }else if(b =='C'){
        cout<<"G"<<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 b;
      |   ^~~~~~
a.cc:5:3: note: suggested alternatives:
In file included from /usr/include/c++/14/iosfwd:41,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
In file included 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:
/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 >> b ;
      |   ^~~
      |   std::cin
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:7:10: error: 'b' was not declared in this scope
    7 |   cin >> b ;
      |          ^
a.cc:10:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |     cout<<"T"<<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:10:16: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |     cout<<"T"<<endl;
      |                ^~~~
      |                std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:12:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   12 |         cout<<"A"<<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:12:20: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   12 |         cout<<"A"<<endl;
      |                    ^~~~
      |                    std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:14:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   14 |         cout<<"C"<<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:14:20: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   14 |         cout<<"C"<<endl;
      |                    ^~~~
      |                    std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:16:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |         cout<<"G"<<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:16:20: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   16 |         cout<<"G"<<endl;
      |                    ^~~~
      |                    std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~