serial number generator program

[Code Doc]

Not sure if this improves the speed of MarkT's code, but it does seem to knock out 4 looping iterations:

Option Explicit

Private Sub Command1_Click()
    MsgBox GenerateSerialNumber
End Sub

Private Function GenerateSerialNumber() As String
Dim strChar(3) As String, i As Integer
Randomize
For i = 0 To 3
    If i < 3 Then
        strChar(i) = Chr(Int(Rnd() * 26) + 65)
    Else
        strChar(i) = Format$(Int(Rnd() * 100000), "00000")
    End If
Next i
GenerateSerialNumber = Join(strChar, "")
End Function

[MarkT]

Not sure if this improves the speed of MarkT's code, but it does seem to knock out 4 looping iterations:

I thought about doing it that way but decided to do a random digit as each spot. If you just do one random number for the last five digit you will end up with a lot of low numbers that will have a number of zeros padding them.

[Code Doc]

I thought about doing it that way but decided to do a random digit as each spot. If you just do one random number for the last five digits you will end up with a lot of low numbers that will have a number of zeros padding them.

Hmmm... I generated 100,000 random 5-digit numbers this way several times and the average is always very near 50,000 and sometimes over 50,000. To me, that indicates no small number bias whatsoever. Give it a try:

Private Sub Command1_Click()
Dim Sum As Single, Num As Long
Num = 100000
For i = 1 To Num
    Call GenerateSerialNumber
    Sum = Sum + CSng(Right$(GenerateSerialNumber, 5))
Next
MsgBox Format$(Sum / Num, "##,###.##")
End Sub

Private Function GenerateSerialNumber() As String
Dim strChar(3) As String
For i = 0 To 3
    If i < 3 Then
        strChar(i) = Chr(Int(Rnd() * 26) + 65)
    Else
        strChar(i) = Format$(Int(Rnd() * 100000), "00000")
    End If
Next i
GenerateSerialNumber = Join(strChar, "")
End Function

Private Sub Form_Load()
Randomize
End Sub

If a distribution of random 5-digit numbers were biased toward small numbers (and thus not random), would not the mean of the distribution have to be significantly less than the theoretical mean of 50,000?

[dilettante]

Well I'd probably use something more like:

Option Explicit

Private Type GUID
    Data1_Lo As Integer
    Data1_Hi As Integer
    Data2 As Integer
    Data3 As Integer
    Data4_0To3 As Long
    Data4_4To7 As Long
End Type

Private Declare Function CoCreateGuid Lib "OLE32.DLL" (pGuid As GUID) As Long

Private Function GenSerial() As String
    Dim udtGUID As GUID
    Dim intA As Integer
    
    If CoCreateGuid(udtGUID) Then
        GenSerial = "*error*"
    Else
        intA = Asc("A")
        With udtGUID
            GenSerial = _
                    Chr$(intA + (.Data1_Lo And &H7FFF) Mod 26) _
                  & Chr$(intA + (.Data2 And &H7FFF) Mod 26) _
                  & Chr$(intA + (.Data3 And &H7FFF) Mod 26) _
                  & Format$((.Data4_4To7 And &H7FFFFFFF) Mod 100000, "00000")
        End With
    End If
End Function

Private Sub cmdGenerate_Click()
    txtSerial.Text = GenSerial()
End Sub