/in/foo.cc: In function 'int _2to10(std::__cxx11::string)':
/in/foo.cc:6:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++)
              ~^~~~~~~~~
/in/foo.cc:8:9: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ret;
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:17: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<_2to10(s);
                 ^