Date Drop Down List

int year, month;
protected void Page_Load(object sender, EventArgs e)
{
DateTime tnow = DateTime.Now;
ArrayList AlYear = new ArrayList();
int i;
for (i = 2002; i <= 2012; i++)
AlYear.Add(i);
ArrayList AlMonth = new ArrayList();
for (i = 1; i <= 12; i++)
AlMonth.Add(i);
if (!this.IsPostBack)
{
DropDownList1.DataSource = AlYear;
DropDownList1.DataBind();
DropDownList1.SelectedValue = tnow.Year.ToString();
DropDownList2.DataSource = AlMonth;
DropDownList2.DataBind();
DropDownList2.SelectedValue = tnow.Month.ToString();
year = Int32.Parse(DropDownList1.SelectedValue);
month = Int32.Parse(DropDownList2.SelectedValue);
BindDays(year, month);
DropDownList3.SelectedValue = tnow.Day.ToString();
}
Label1.Text = "You select date:" + DropDownList1.SelectedValue + "year" + DropDownList2.SelectedValue + "month" + DropDownList3.SelectedValue;
}

//judge leap year
private bool CheckLeap(int year)
{
if ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0))
return true;
else return false;
}

//binding every month day
private void BindDays(int year, int month)
{
int i;
ArrayList AlDay = new ArrayList();

switch (month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
for (i = 1; i <= 31; i++)
AlDay.Add(i);
break;
case 2:
if (CheckLeap(year))
{
for (i = 1; i <= 29; i++)
AlDay.Add(i);
}
else
{
for (i = 1; i <= 28; i++)
AlDay.Add(i);
}
break;
case 4:
case 6:
case 9:
case 11:
for (i = 1; i <= 30; i++)
AlDay.Add(i);
break;
}
DropDownList3.DataSource = AlDay;
DropDownList3.DataBind();
}
//select year
public void DropDownList1_SelectedIndexChanged(object sender, System.EventArgs e)
{
year = Int32.Parse(DropDownList1.SelectedValue);
month = Int32.Parse(DropDownList2.SelectedValue);
BindDays(year, month);
}

//select month
public void DropDownList2_SelectedIndexChanged(object sender, System.EventArgs e)
{
year = Int32.Parse(DropDownList1.SelectedValue);
month = Int32.Parse(DropDownList2.SelectedValue);
BindDays(year, month);
}
}