How to remove all rows in a DataGridView

I have a DataGridView that takes data from a textbox that user inputs. Then, a button that lets user save all rows to database. After saving, I want to remove all rows in the DataGridView. However, the DataGridView always keeps one row undeleted. My code is:

{

   for (int i = 0; i < dataGridView1.Rows.Count; i++)

   {

       dataGridView1.Rows.RemoveAt(i);

   }

}

What is wrong with my code?

Thanks,