Perulangan Do Until Pada VB.Net

Public Class Perulangan

    Private Sub Perulangan_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim a As Byte
        a = 10
        Do Until a = 0
            ComboBox1.Items.Add(a)
            a -= 1
        Loop
        Dim c As Byte
        c = 65
        Do Until a = 91
            ComboBox3.Items.Add(Chr(a))
            c = Val(c + 1)
        Loop
        Dim b As Integer
        b = 1
        Do Until b = 11
            ComboBox2.Items.Add(b)
            b += 1
        Loop
    End Sub
End Class