question about "new" and "delete" ?

[jack]

the following code can be run and can generate result:
a[9]=10;
what happend there?
int main()
{
  double *a= new double[10];
  for(int i=0;i<10;i++){
    a[i]=i+1;
  }
  delete [] a;
  cout << a[9] << endl;
  return 0;
}