/in/foo.cc: In function 'int ff(int)':
/in/foo.cc:15:22: error: 'sqrt' was not declared in this scope
   15 |  for (int i = 2; i < sqrt(n); i++)
      |                      ^~~~
/in/foo.cc: In function 'int f(char)':
/in/foo.cc:12:1: warning: control reaches end of non-void function [-Wreturn-type]
   12 | }
      | ^