Display Number of Days in a Month In ASP.Net when month is selected from DropDownList

Try

        <asp:DropDownList ID="ddlMonths" runat="server" AutoPostBack ="true" OnSelectedIndexChanged ="Month_Changed">
            <asp:ListItem Text ="Please select" Value ="0"></asp:ListItem>
            <asp:ListItem Text ="January" Value ="1"></asp:ListItem>
            <asp:ListItem Text ="February" Value ="2"></asp:ListItem>
            <asp:ListItem Text ="March" Value ="3"></asp:ListItem>
            <asp:ListItem Text ="April" Value ="4"></asp:ListItem>
            <asp:ListItem Text ="May" Value ="5"></asp:ListItem>
            <asp:ListItem Text ="June" Value ="6"></asp:ListItem>
            <asp:ListItem Text ="July" Value ="7"></asp:ListItem>
            <asp:ListItem Text ="August" Value ="8"></asp:ListItem>
            <asp:ListItem Text ="September" Value ="9"></asp:ListItem>
            <asp:ListItem Text ="October" Value ="10"></asp:ListItem>
            <asp:ListItem Text ="November" Value ="11"></asp:ListItem>
            <asp:ListItem Text ="December" Value ="12"></asp:ListItem>
        </asp:DropDownList>
        <br />
        <asp:TextBox ID="txtMonths" runat="server"></asp:TextBox>

Protected Sub Month_Changed(sender As Object, e As EventArgs)
	Dim month As Integer = Integer.Parse(ddlMonths.SelectedItem.Value)
	txtMonths.Text = DateTime.DaysInMonth(DateTime.Now.Year, month).ToString()
End Sub