C#

// insert at Class scope in your UserControl or sub-classed WinForm container

protected override CreateParams CreateParams
{
    get
    {
        CreateParams cp = base.CreateParams;
        cp.ExStyle = cp.ExStyle | 0x2000000;
        return cp;
    }
}

        database db = new database();        DataTable tbl = new DataTable();
        private void AutoNumber()
        {
            tbl.Clear();
            tbl = db.readData("Select max (Des_ID) from Deserved", "");


// in the next line the error coming out


            if ((tbl.Rows[0][0].ToString() == DBNull.Value.ToString()))
            {
                txtID.Text = "1";
            }
            else
            {
                txtID.Text = (Convert.ToInt32(tbl.Rows[0][0]) + 1).ToString();
            }
            NudPrice.Value = 1;
            DtbDate.Text = DateTime.Now.ToShortDateString();
            txtNotes.Clear();
            btnAdd.Enabled = true;
            btnNew.Enabled = true;
            btnDelete.Enabled = false;
            btnDeleteAll.Enabled = false;
            btnSave.Enabled = false;

List<string> collection = new List<string>() {"", "ghjg", "jkgh", ""};
var indexOf = collection.Select((value, index) => new { value, index })
						.Where(pair => string.IsNullOrEmpty(pair.value))
						.Select(pair => pair.index);
foreach (var item in indexOf)
{
	Console.WriteLine(item);
}

private void button1_Click(object sender, EventArgs e)
{
    string Arquivo = @"D:\Diversos\Antares\Relatório.xlsx";
    Excel.Application xlApp;
    Excel.Workbook xlWorkBook;
    Excel.Worksheet xlWorkSheet;
    object misValue = System.Reflection.Missing.Value;

    //Cria uma planilha temporária na memória do computador
    xlApp = new Excel.Application();
    xlWorkBook = xlApp.Workbooks.Add(misValue);
    xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
    xlWorkSheet.Range[ws.Cells[1, 1], ws.Cells[1, 4]].Merge();
    xlWorkSheet.Visible = XlSheetVisibility.xlSheetVisible;

    //incluindo dados
    xlWorkSheet.Cells[1, 1] = "Dados do cliente:";
    //            xlWorkSheet.Cells[1, 2] = textBox1.Text;
    //            xlWorkSheet.Cells[1, 3] = textBox2.Text;
    //            xlWorkSheet.Cells[1, 4] = textBox3.Text;

    //Salva o arquivo de acordo com a documentação do Excel.
    xlWorkBook.SaveAs(Arquivo, Excel.XlFileFormat.xlWorkbookDefault, misValue, misValue, misValue, misValue,
    Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
    xlWorkBook.Close(true, misValue, misValue);
    xlApp.Quit();

}

String str = "dt.Rows[i][3]";

For (int i=0; dt.Rows.Count; i++)
{
    str;
}