Imports System.Text
Public Class Form1

    Dim i As Integer
    Dim str As String
    Dim std As String
    Dim n As Integer = 1


    Private Const uppercase As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    Private Const lowercase As String = "abcdefghijklmnopqrstuvwxyz"

    Private Function genmask(ByVal mask As String) As String
        Dim output As New StringBuilder
        Dim random As New Random()
        For c As Integer = 0 To mask.Length - 1
            If (mask(c) = "@") Then
                output.Append(random.Next(0, 9))
            ElseIf (mask(c) = "$") Then
                output.Append(uppercase(random.Next(0, uppercase.Length())))
            ElseIf (mask(c) = "#") Then
                output.Append(lowercase(random.Next(0, lowercase.Length())))
            Else
                output.Append(mask(c))
            End If
        Next
        Return output.ToString
    End Function


    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        While n <= TextBox1.Text
        str = (genmask("Walter-$#@$#-#s@d"))   ' input mask
        Dim ss As New ListViewItem
        ss.Text = (str)
        ListView1.Items.Add(ss)
        n += 1
        End While
    End Sub
End Class