/in/foo.cc: In function 'int main()':
/in/foo.cc:8:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<=a.size()-1;i++)
              ~^~~~~~~~~~~~
/in/foo.cc:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<=b.size()-1;i++)
              ~^~~~~~~~~~~~
/in/foo.cc:18:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=a.size();i++)
              ~^~~~~~~~~~
/in/foo.cc:20:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=1;j<=b.size();j++)
                ~^~~~~~~~~~