foo.cc: In function 'int main()':
foo.cc:12:5: error: 'vector' was not declared in this scope
   12 |     vector<int> a(n);
      |     ^~~~~~
foo.cc:2:1: note: 'std::vector' is defined in header '<vector>'; did you forget to '#include <vector>'?
    1 | #include <iostream>
  +++ |+#include <vector>
    2 | 
foo.cc:12:12: error: expected primary-expression before 'int'
   12 |     vector<int> a(n);
      |            ^~~
foo.cc:13:12: error: expected primary-expression before 'int'
   13 |     vector<int> b(n);
      |            ^~~
foo.cc:17:14: error: 'a' was not declared in this scope
   17 |       cin >> a[i];
      |              ^
foo.cc:20:14: error: 'b' was not declared in this scope
   20 |       cin >> b[j];
      |              ^
foo.cc:25:12: error: 'a' was not declared in this scope
   25 |       sort(a.rbegin(), a.rend());
      |            ^
foo.cc:25:7: error: 'sort' was not declared in this scope; did you mean 'short'?
   25 |       sort(a.rbegin(), a.rend());
      |       ^~~~
      |       short
foo.cc:26:12: error: 'b' was not declared in this scope
   26 |       sort(b.rbegin(), b.rend());
      |            ^