Language: C++

#include<iostream>
#include<string>

int main(){
  string S;
  cin >> S;
  
  if(S=="Sunny") cout << "Cloudy" << endl;
  if(S=="Cloudy") cout << "Rainy" << endl;
  if(S=="Rainy") cout << "Sunny" << 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;
      |   ^~~~~~
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:6:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |   cin >> S;
      |   ^~~
      |   std::cin
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:6:10: error: 'S' was not declared in this scope
    6 |   cin >> S;
      |          ^
a.cc:8:18: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    8 |   if(S=="Sunny") cout << "Cloudy" << 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:8:38: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    8 |   if(S=="Sunny") cout << "Cloudy" << endl;
      |                                      ^~~~
      |                                      std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:9:19: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    9 |   if(S=="Cloudy") cout << "Rainy" << 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:9:38: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    9 |   if(S=="Cloudy") cout << "Rainy" << endl;
      |                                      ^~~~
      |                                      std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:10:18: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |   if(S=="Rainy") cout << "Sunny" << 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:10:37: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |   if(S=="Rainy") cout << "Sunny" << endl;
      |                                     ^~~~
      |                                     std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~