Language: C++

#include <iostream>
#include <string>

int main()	{
  string a, b, c;
  cin >> a >> b >> c;
  int x = a.length(), y = b.length(), z = c.length();
  if (a[x - 1] == b[0] && b[y - 1] == c[0])
    cout << "YES" << endl;
  else
    cout << "NO" << 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 a, b, c;
      |   ^~~~~~
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 >> a >> b >> c;
      |   ^~~
      |   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: 'a' was not declared in this scope
    6 |   cin >> a >> b >> c;
      |          ^
a.cc:6:15: error: 'b' was not declared in this scope
    6 |   cin >> a >> b >> c;
      |               ^
a.cc:6:20: error: 'c' was not declared in this scope
    6 |   cin >> a >> b >> c;
      |                    ^
a.cc:8:29: error: 'y' was not declared in this scope
    8 |   if (a[x - 1] == b[0] && b[y - 1] == c[0])
      |                             ^
a.cc:9:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    9 |     cout << "YES" << 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:9:22: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    9 |     cout << "YES" << endl;
      |                      ^~~~
      |                      std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:11:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   11 |     cout << "NO" << 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:11:21: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   11 |     cout << "NO" << endl;
      |                     ^~~~
      |                     std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~