Language: C++

#include <iostream>
#include <vector>

int main(){
	vector<int> A(5);
	for(int i = 0; i < 5; i++){
		cin >> A.at(i);
	}
	int K;
	cin >> K;
	int ans = A.at(4) - A.at(0);
	if(ans > K) cout << ":(" << endl;
	else cout << "Yay!" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:5:9: error: 'vector' was not declared in this scope
    5 |         vector<int> A(5);
      |         ^~~~~~
a.cc:5:9: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:2:
/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:5:16: error: expected primary-expression before 'int'
    5 |         vector<int> A(5);
      |                ^~~
a.cc:7:17: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |                 cin >> A.at(i);
      |                 ^~~
      |                 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:7:24: error: 'A' was not declared in this scope
    7 |                 cin >> A.at(i);
      |                        ^
a.cc:10:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
   10 |         cin >> K;
      |         ^~~
      |         std::cin
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:11:19: error: 'A' was not declared in this scope
   11 |         int ans = A.at(4) - A.at(0);
      |                   ^
a.cc:12:21: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   12 |         if(ans > K) cout << ":(" << 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:12:37: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   12 |         if(ans > K) cout << ":(" << 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:13:14: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   13 |         else cout << "Yay!" << 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:13:32: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   13 |         else cout << "Yay!" << endl;
      |                                ^~~~
      |                                std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~