foo.cc: In function 'int main()':
foo.cc:9:16: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for(int i=a; i<b; i++) 
               ~^~

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