/in/foo.cc: In function 'int main()':
/in/foo.cc:19:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<s.size();++i)
                 ~^~~~~~~~~
/in/foo.cc:24:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(j=i;j<s.size()&&isdigit(s[j]);++j)
                     ~^~~~~~~~~