VB.netで乱数を生成

VB.netで乱数を生成して、テキストボックスに文字列化するコード

    Sub GenRandom()
        Dim si As String = ""
        Dim n As Integer
        For n = 0 To 6 - 1
            Dim i As Integer = r.Next(10)
            si &= i.ToString()
        Next
        TextBox1.Text = si


        Dim arrayLarge() As String = {"A", "B", "C", "D", "E", "F", "G", "H",
                                        "I", "J", "K", "L", "M", "N", "O", "P",
                                        "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"}
        Dim sl As String = ""
        For n = 0 To 5 - 1
            Dim c As Integer = r.Next(26)
            sl &= arrayLarge(c)
        Next
        TextBox2.Text = sl

        Dim arraySmall() As String = {"a", "b", "c", "d", "e", "f", "g", "h",
                                        "i", "j", "k", "l", "m", "n", "o", "p",
                                        "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"}
        Dim ss As String = ""
        For n = 0 To 5 - 1
            Dim c As Integer = r.Next(26)
            ss &= arraySmall(c)
        Next
        TextBox3.Text = ss
    End Sub