Validate field in VBA

Question

In Mozambique there is a unique tax identification number (Nuit), and this number takes 9 digits.
How an application would look to validate the Nuit meeting the following conditions?

• If there are more(+) or less(-) than nine(9) digits, say "invalid Nuit."

• Should accept only numbers, if they are not numbers say "please type only numbers"

I have here the algorithm:

Private Sub CommandButton1_Click()

v = validarnuit(TextBox1.Text)
MsgBox v

End Sub
Function validarnuit(nuit)
Dim cd As Double
Dim valido As String
valido = "Nuit Invalido"
If Len(nuit) = 9 Then
If IsNumeric(nuit) Then
If nuit <> 0 Then

cd = Mid(nuit, 8, 1) * 2
cd = cd + Mid(nuit, 7, 1) * 3 + _
cd = cd + Mid(nuit, 6, 1) * 4 + _
cd = cd + Mid(nuit, 5, 1) * 5 + _
cd = cd + Mid(nuit, 4, 1) * 6 + _
cd = cd + Mid(nuit, 3, 1) * 7 + _
cd = cd + Mid(nuit, 2, 1) * 2 + _
cd = cd + Mid(nuit, 1, 1) * 3 + _
cd = 11 - (cd Mod 11)
If cd = 9 Then
valido = "good"
End If
End If
End If
End If
validarnuit = valido
End Function

If the cd fore equal to 11, is false and does not validate; if it is equal to 10 also does not validate; only validates if cd is equal to 9. Image if the division is equal to 2, this would be 11-2 = cd 9 and validate. I tried using this code above but did not give 9. Does anyone have an effective idea of how to do this?

Answer 1

(the following reply relates to this editing)

Assuming you are receiving data on TextBox can use the function Len to determine the size of a string:

tamanhoEsperado = 9 ' Tamanho do número esperado 
tamanho = Len(TextBox.Value)
If (tamanho > tamanhoEsperado) Then
    ' Invalido
ElseIf (tamanho < tamanhoEsperado) Then
    ' Invalido
Else
    ' Válido
End If

To be able to determine if they are just digits, the VBA has the function IsNumeric which you can use as follows:

If(IsNumeric(TextBox.Value)) Then
     ' São apenas números, grave na base de dados
EndIf

Edit:

To enter the field in the database:

' Abra a ligação
Set conn = New ADODB.Connection
conn.ConnectionString = "" 'Coloque aqui a sua connection string
conn.Open

' Crie a instrução INSERT INTO.
statement = "INSERT INTO nuit " & _
    "(nuit) " & _
    " VALUES (" & _
    "'" & txtnuit.Value & "', " & _
    ")"

' Execute a instrução.
conn.Execute statement, , adCmdText

' Feche a ligação.
conn.Close