VBA代码编写在窗体的文本框TextBox1中输入不大于9的整数 然后计算其阶乘后在文本框TextBox2中输出 怎么编

Private Sub CommandButton1_Click()

Dim a, b1, b2, i, tmp

Set b1 = Me.TextBox1

Set b2 = Me.TextBox2

a = b1.Text

If Len(a) = 0 Then tmp = "#Len = 0": GoTo 1000

If Not IsNumeric(a) Then tmp = "#Not Is Number": GoTo 1000

a = a * 1

If Int(a) <> a Then tmp = "#not Integer": GoTo 1000

If a < 1 Or a > 9 Then tmp = "#" & IIf(a < 1, "<1", ">9"): GoTo 1000

tmp = a

For i = a - 1 To 2 Step -1

tmp = tmp * i

Next

1000:

b2.Text = tmp

End Sub