foo.cc: In function 'int main()':
foo.cc:4:7: error: variable or field 'a' declared void
  void a;
       ^
foo.cc:5:7: error: 'a' was not declared in this scope
  cin<<a;
       ^

自豪的采用 HydroJudger 进行评测(github.com/hydro-dev/HydroJudger)