/in/foo.cc: In function 'int main()':
/in/foo.cc:13:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++){
              ~^~~~~~~~~
/in/foo.cc:15:20: warning: 'n' may be used uninitialized in this function [-Wmaybe-uninitialized]
   else a[++n]=x,x=0;
                    ^