Need to know what did I do wrong in this VB code....

Public Class Form1
    Dim x As Integer = 1
    Dim y As Integer = 1
    Dim z As String
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Do
            z = ""
            Do
                z = z & (y * x) & " "

                y = y + 1

            Loop While (y <= 10)
            x = x + 1
            lstBox.Items.Add(z)
        Loop While (x <= 10)

    End Sub
End Class