foo.cc: In function 'int main()':
foo.cc:18:9: warning: 'i' is used uninitialized in this function [-Wuninitialized]
  int a[i];
         ^
foo.cc:19:9: warning: 'j' is used uninitialized in this function [-Wuninitialized]
  int b[j];
         ^

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