C#

DateTime base = DateTime.Parse("1.1.1900");
DateTime fromExcel = base.AddDays(serial);

class MainForm
{
  public static MainForm Instance
  {
    get
    {
      if (MainForm.instance == null)
        MainForm.instance = new MainForm();
      return MainForm.instance;
    }
  }
  private static MainForm instance;

  protected MainForm()
  {
  }
}

DataGridTableStyle style = new DataGridTableStyle();
style.MappingName = "myDataTable";

DataGridColumnStyle colStyle = new DataGridTextBoxColumn();
colStyle.MappingName = "col1";
style.GridColumnStyles.Add(colStyle);

colStyle = new DataGridTextBoxColumn();
colStyle.MappingName = "col2";
style.GridColumnStyles.Add(colStyle);

colStyle = new DataGridTextBoxColumn();
colStyle.MappingName = "col3";
colStyle.Width = 0;
style.GridColumnStyles.Add(colStyle);

dataGrid1.TableStyles.Add(style);

using (StreamWriter writer = new StreamWriter("file.txt", true,
  Encoding.UTF8))
  writer.WriteLine("This is a single line.");
}