/in/foo.cc: In function 'int main()':
/in/foo.cc:30:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(i=0;i<ans.size();i++)
            ~^~~~~~~~~~~
/in/foo.cc: In function 'std::__cxx11::string px(std::__cxx11::string&)':
/in/foo.cc:41:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<aaa.length();i++)
          ~^~~~~~~~~~~~~