Public Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        For index As Integer = 1 To 10
            ListBox1.Items.Add(index)

            If index = 5 Then
                Exit For
            End If
        Next
    End Sub
End Class