title: getting datagridview last row index
body: <p>i'm trying to get the last row but the problem is....see my
  code</p>
  
  <pre><code>Int32 index=dataGridveiw1.Rows.Count; // this is count start 1,2,3,4,5,6
  
  sum3=txt_lotweight.Text-txt_balanceweight.Text;
  sum4=datagridview1.Rows[index].Cells["rollweight"].Value-sum3;
  </code></pre>
  
  <p>how to minus gridview last row value to sum3  in this code error
  will come rows index not found because rows count start from 1  and
  when i subtract rows value to sum3 its start from 0</p>
  
  <p>so how to get last row of gridview</p>