How do I make datagridview cells text changed event

private void grid1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
           {
               if ( grid1.CurrentCell.ColumnIndex == 3)
               {
                   TextBox tb = (TextBox)e.Control;
                   tb.TextChanged += new EventHandler(tb_TextChanged);
               }

              if (grid1.CurrentCell.ColumnIndex == 5)
              {
                  TextBox tb5 = (TextBox)e.Control;
                  tb5.TextChanged += new EventHandler(tb5_TextChanged);
              }
              if (grid1.CurrentCell.ColumnIndex == 4)
              {
                  TextBox tb4 = (TextBox)e.Control;
                  tb4.TextChanged += new EventHandler(tb4_TextChanged);
              }
           }

tb5_TextChanged , tb4_TextChanged , tb3_TextChanged all same code 

<pre>void tb5_TextChanged(object sender, EventArgs e)
        {
            var c5 = (sender as TextBox).Text;

            double No3 = 0;
            double No2 = 0;
            double No1 = 0;

            if (grid1.CurrentCell.ColumnIndex == 5)
                label8.Text = c5;
            
            if (grid1.CurrentCell.Value != null)
            {
                for (int i = 0; i < grid1.RowCount; i++)
                {
                    if (grid1.Rows[i].Cells[0].Value.ToString() != null && grid1.Rows[i].Cells[1].Value.ToString() != null)
                    {
                        if (Double.TryParse(label6.Text, out No2) && Double.TryParse(label7.Text, out No1) && Double.TryParse(label8.Text, out No3))
                            grid1.Rows[i].Cells[6].Value = (No1 * No2 - No3).ToString();
                    }
                }
            }
             
        }