foo.cc: In function 'int main()':
foo.cc:9:3: error: 'f' was not declared in this scope
   f[i] = a[i];
   ^
foo.cc:14:3: error: expected ';' before 'b'
   b[x]++;
   ^

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