/in/foo.cc: In function 'int main()':
/in/foo.cc:11:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();)
              ~^~~~~~~~~
/in/foo.cc:27:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(isdigit(s[i])&&i<s.size())x=x*10+s[i]-'0',i++,f=1;
                          ~^~~~~~~~~