Basic. Ошибки в программе. Тема Массивы

For i = 0 To UBound(a) 
 m = m + Format(a(i), "0.0") + Space(2)

Option Strict On 
Option Explicit On 
Imports System.Math 
Public Class Form1 
 Dim x() As Single 
 Dim y() As Single 
 Dim P As Single 
 
 Sub vvodRnd(ByRef x() As Single) 
 Dim i As Integer 
 Randomize() 
 ReDim x(19) 
 For i = 0 To 19 
 x(i) = -3 + 12 * Rnd() 
 Next i 
 End Sub 
 Sub vivod(ByVal Z As Double, ByVal T As TextBox) 
 T.Text = Format(Z, "0.0") 
 End Sub 
 Sub vivodM(ByRef a() As Single, ByRef LB As ListBox) 
 Dim i As Integer 
 Dim m As String = "" 
 For i = 0 To UBound(a) 
 m = m + Format(a(i), "0.0") + Space(2) 
 Next i 
 If m = "" Then m = "массив пуст" 
 LB.Items.Add(m) 
 End Sub 
 Sub NewM(ByRef x() As Single, ByRef y() As Single, ByRef P As Single) 
 Dim b, tmp As Single 
 P = 1 
 b = 1 
 For i = 0 To 19 
 If (i Mod 2) = 0 Then 
 P = P * x(i) 
 Else 
 b = b * x(i) 
 End If 
 Next i 
 '::: Перестановки 
 For i = 1 To 19 
 For j = i + 1 To 19 
 If x(i) < 0 And x(j) > 0 Then 
 tmp = x(i) 
 x(i) = x(j) 
 x(j) = tmp 
 End If 
 Next j 
 Next i 
 End Sub 
 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 
 ListBox1.Items.Clear() 
 ListBox2.Items.Clear() 
 vvodRnd(x) 
 NewM(x, y, P) 
 vivodM(x, ListBox1) 
 vivodM(y, ListBox2) 
 vivod(P, TextBox1) 
 End Sub 
 Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click 
 End 
 End Sub 
End Class