/in/foo.cc: In function 'int main()':
/in/foo.cc:9:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0,j=a.size()-1;i<a.size(),j>=0;i++,j--){
                           ~^~~~~~~~~
/in/foo.cc:9:28: warning: value computed is not used [-Wunused-value]