Listing Program Looping Di VB.Net 2008

Public Class LOOPING

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim z As Byte
        ListBox1.Items.Clear()
        z = 1
        Do Until z = 11
            ListBox1.Items.Add(z)
            z = z + 1

        Loop
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim x As Byte
        x = 1
        Do While x <= 10
            ListBox2.Items.Add(x)
            x = x + 1

        Loop
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim y As Integer
        For y = 20 To 1 Step -5
            ListBox3.Items.Add(y & "x")

        Next

    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Dim b As Byte
        b = 1
        While b <= 10
            ListBox4.Items.Add(b)
            b = b + 1

        End While

    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        Dim a As Integer
        For a = 1 To 4
            ListBox5.Items.Add("STMIK")

        Next
    End Sub