/in/foo.cc: In function 'int main()':
/in/foo.cc:9:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<=a.size();i++)
              ~^~~~~~~~~~
/in/foo.cc:8:7: warning: unused variable 'ok' [-Wunused-variable]
  bool ok=0;
       ^~