/in/foo.cc: In function 'int main()':
/in/foo.cc:17:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<a.size();i++)
               ~^~~~~~~~~
/in/foo.cc:30:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i=0;i<a.size();i++)
                ~^~~~~~~~~