foo.cc: In function 'int main()':
foo.cc:5:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    5 |     cout << 0 << '\n';
      |     ^~~~
      |     std::cout
In file included from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:146,
                 from foo.cc:1:
/usr/include/c++/13/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~