/in/foo.cc: In function 'int main()':
/in/foo.cc:23:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(j==x.size())
       ~^~~~~~~~~~
/in/foo.cc:29:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(j==x.size())
      ~^~~~~~~~~~