/in/foo.cc: In function 'int main()':
/in/foo.cc:29:3: error: 'f' was not declared in this scope
   f[i] = i * f[i - 1] + (i & 1 ? -1 : 1);
   ^
/in/foo.cc:30:2: error: 'cout' was not declared in this scope
  cout << n;
  ^~~~
/in/foo.cc:30:2: note: suggested alternative:
In file included from /in/foo.cc:3:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~