foo.cc: In function 'int fibonacci(int)':
foo.cc:16:9: error: 'f' was not declared in this scope
  return f(n - 1) + f(n - 2);
         ^
foo.cc: In function 'int main()':
foo.cc:21:8: error: 'f' was not declared in this scope
  int s=f(n);
        ^
foo.cc:21:6: warning: unused variable 's' [-Wunused-variable]
  int s=f(n);
      ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。