foo.cc: In function 'int main()':
foo.cc:29:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(i<s.size()){
           ~^~~~~~~~~
foo.cc:27:10: warning: unused variable 'ch' [-Wunused-variable]
     char ch;
          ^~

自豪的采用jd5进行评测(github.com/masnn/jd5)