This is a simple VB6 function to generate random numbers in the specified range, without repeating any numbers.
New, and only briefly tested. Use at your own risk. :)
- Option Explicit
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Private UsedNumber As New Collection
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Private Const MaxAttempts As Long = 150
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Private Const Zero As Long = 0
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Private Const One As Long = 1
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Public Function RandomNonRepeatingBetween(ByVal LowerLimit As Long, ByVal UpperLimit As Long) As Long
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' Generate a pseudo-random number between the specified bounds.
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' Never return one which has already been used.
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' Don't forget to use Randomize at least once before calling
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' this function (but not EVERY time, if calling repeatedly).
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' The record of used numbers will be cleared only when the
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' caller specifically requests it by passing zero as both the
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' upper and lower bounds.
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' If it is not possible to satisfy the request (for instance,
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' if all numbers in the requested range have already been
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' used, then error 17 ("Can't perform requested operation")
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' will be raised. Caller should allow for this and handle
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' it as appropriate.
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' Note, for the moment it will simply try up to 150 times, I
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' haven't worked out the code yet to do a proper check for
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' whether any numbers are left in the range.
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' If lower/upper limit are backward, swap them around.
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Dim Temp As Long
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Dim Attempts As Long
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If LowerLimit > UpperLimit Then
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Temp = LowerLimit
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LowerLimit = UpperLimit
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UpperLimit = Temp
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End If
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' Clear memory if caller requests it.
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If LowerLimit = Zero And UpperLimit = Zero Then
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Do While UsedNumber.Count > Zero
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UsedNumber.Remove One
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Loop
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End If
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On Error Resume Next
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Do
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Temp = LowerLimit + Rnd * (UpperLimit - LowerLimit)
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UsedNumber.Add Temp, Format(Temp)
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If Err.Number = Zero Then
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RandomNonRepeatingBetween = Temp
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Exit Do
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End If
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Err.Clear
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Attempts = Attempts + One
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Loop While Attempts < MaxAttempts
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Err.Clear
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On Error GoTo 0
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End Function
