foo.cc: In function 'void Count()':
foo.cc:7:6: warning: left operand of comma operator has no effect [-Wunused-value]
  i,j=0;
      ^
foo.cc:8:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<a.length();i++)
          ~^~~~~~~~~~~

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