Language: C++

#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0;i < n;i++)
#define VSORT(v) sort(v.begin(), v.end());
#define VSORTR(v) sort(v.rbegin(), v.rend());

int dy[]={0, 0, 1, -1, 0};
int dx[]={1, -1, 0, 0, 0};

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	vector <int> v(3);
	REP(i, 3) cin >> v[i];
	VSORT(v);

	ostringstream v21s;
	v21s << v[2] << v[1];

	int v21i;
	istringstream v21;
	v21 = istringstream(v21s.str());
	v21 >> v21i;

	cout << v21i + v[0] << "\n";
}

Compiler output:
a.cc: In function 'int main()':
a.cc:10:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
   10 |         cin.tie(0);
      |         ^~~
      |         std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 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:11:9: error: 'ios' has not been declared
   11 |         ios::sync_with_stdio(false);
      |         ^~~
a.cc:13:9: error: 'vector' was not declared in this scope
   13 |         vector <int> v(3);
      |         ^~~~~~
a.cc:13:9: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53:
/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:13:17: error: expected primary-expression before 'int'
   13 |         vector <int> v(3);
      |                 ^~~
a.cc:14:26: error: 'v' was not declared in this scope
   14 |         REP(i, 3) cin >> v[i];
      |                          ^
a.cc:15:15: error: 'v' was not declared in this scope
   15 |         VSORT(v);
      |               ^
a.cc:3:23: note: in definition of macro 'VSORT'
    3 | #define VSORT(v) sort(v.begin(), v.end());
      |                       ^
a.cc:3:18: error: 'sort' was not declared in this scope; did you mean 'std::sort'?
    3 | #define VSORT(v) sort(v.begin(), v.end());
      |                  ^~~~
a.cc:15:9: note: in expansion of macro 'VSORT'
   15 |         VSORT(v);
      |         ^~~~~
In file included from /usr/include/c++/14/algorithm:86,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/pstl/glue_algorithm_defs.h:296:1: note: 'std::sort' declared here
  296 | sort(_ExecutionPolicy&& __exec, _RandomAccessIterator __first, _RandomAccessIterator __last);
      | ^~~~
a.cc:17:9: error: 'ostringstream' was not declared in this scope; did you mean 'std::ostringstream'?
   17 |         ostringstream v21s;
      |         ^~~~~~~~~~~~~
      |         std::ostringstream
In file included from /usr/include/c++/14/bits/localefwd.h:41,
                 from /usr/include/c++/14/string:45,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/iosfwd:155:41: note: 'std::ostringstream' declared here
  155 |   typedef basic_ostringstream<char>     ostringstream;
      |                                         ^~~~~~~~~~~~~
a.cc:18:9: error: 'v21s' was not declared in this scope
   18 |         v21s << v[2] << v[1];
      |         ^~~~
a.cc:21:9: error: 'istringstream' was not declared in this scope; did you mean 'std::istringstream'?
   21 |         istringstream v21;
      |         ^~~~~~~~~~~~~
      |         std::istringstream
/usr/include/c++/14/iosfwd:152:41: note: 'std::istringstream' declared here
  152 |   typedef basic_istringstream<char>     istringstream;
      |                                         ^~~~~~~~~~~~~
a.cc:22:9: error: 'v21' was not declared in this scope; did you mean 'v21i'?
   22 |         v21 = istringstream(v21s.str());
      |         ^~~
      |         v21i
a.cc:25:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   25 |         cout << v21i + v[0] << "\n";
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~