Non-repeating random number generator?

Question

I created a trivia game using visual basic for applications (Excel) that chooses questions by going through a case statement where the cases are numbers. I have the program randomly select a number from 1 to the max amount of questions there are. Using this method, the game repeats questions.

Is there a way to make something that generates numbers randomly (different results every time) and doesn't repeat a number more than once? And after it's gone through all the numbers it needs to execute a certain code. (I'll put in code that ends the game and displays the number of questions they got right and got wrong)

I thought of a few different ways to do this, however I couldn't even begin to think of what the syntax might be.

Answer 1

I see you have an answer, I was working on this but lost my internet connection. Anyway here is another method.

'// Builds a question bank (make it a hidden sheet)
Sub ResetQuestions()
    Const lTotalQuestions As Long = 300 '// Total number of questions.

    With Range("A1")
        .Value = 1
        .AutoFill Destination:=Range("A1").Resize(lTotalQuestions), Type:=xlFillSeries
    End With

End Sub
'// Gets a random question number and removes it from the bank
Function GetQuestionNumber()
    Dim lCount As Long   

    lCount = Cells(Rows.Count, 1).End(xlUp).Row      

    GetQuestionNumber = Cells(Int(lCount * Rnd + 1), 1).Value

    Cells(lRandom, 1).Delete
End Function

Sub Test()

    Msgbox (GetQuestionNumber)

End Sub

Answer 2

Sounds like you need an Array Shuffler!

Check out the below link - http://www.cpearson.com/excel/ShuffleArray.aspx

Function ShuffleArray(InArray() As Variant) As Variant()
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' ShuffleArray
' This function returns the values of InArray in random order. The original
' InArray is not modified.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
    Dim N As Long
    Dim Temp As Variant
    Dim J As Long
    Dim Arr() As Variant


    Randomize
    L = UBound(InArray) - LBound(InArray) + 1
    ReDim Arr(LBound(InArray) To UBound(InArray))
    For N = LBound(InArray) To UBound(InArray)
        Arr(N) = InArray(N)
    Next N
    For N = LBound(InArray) To UBound(InArray)
        J = CLng(((UBound(InArray) - N) * Rnd) + N)
        Temp = InArray(N)
        InArray(N) = InArray(J)
        InArray(J) = Temp
    Next N
    ShuffleArray = Arr
End Function

Sub ShuffleArrayInPlace(InArray() As Variant)
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' ShuffleArrayInPlace
' This shuffles InArray to random order, randomized in place.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
    Dim N As Long
    Dim Temp As Variant
    Dim J As Long

    Randomize
    For N = LBound(InArray) To UBound(InArray)
        J = CLng(((UBound(InArray) - N) * Rnd) + N)
        If N <> J Then
            Temp = InArray(N)
            InArray(N) = InArray(J)
            InArray(J) = Temp
        End If
    Next N
End Sub

Answer 3

For whatever it's worth here is my stab at this question. This one uses a boolean function instead of numerical arrays. It's very simple yet very fast. The advantage of it, which I'm not saying is perfect, is an effective solution for numbers in a long range because you only ever check the numbers you have already picked and saved and don't need a potentially large array to hold the values you have rejected so it won't cause memory problems because of the size of the array.

Sub UniqueRandomGenerator()
Dim N As Long, MaxNum As Long, MinNum As Long, Rand As Long, i As Long

MinNum = 1        'Put the input of minimum number here
MaxNum = 100      'Put the input of maximum number here
N = MaxNum - MinNum + 1

ReDim Unique(1 To N, 1 To 1)

For i = 1 To N
Randomize         'I put this inside the loop to make sure of generating "good" random numbers
    Do
        Rand = Int(MinNum + N * Rnd)
        If IsUnique(Rand, Unique) Then Unique(i, 1) = Rand:  Exit Do
    Loop
Next
Sheet1.[A1].Resize(N) = Unique
End Sub

Function IsUnique(Num As Long, Data As Variant) As Boolean
Dim iFind As Long

On Error GoTo Unique
iFind = Application.WorksheetFunction.Match(Num, Data, 0)

If iFind > 0 Then IsUnique = False: Exit Function

Unique:
    IsUnique = True
End Function

Answer 4

Here's yet another take. It generates an array of unique, random longs. In this example, I use 1 to 100. It does this by using the collection object. Then you can just do a normal loop through each array element in qArray without the need to randomize more than once.

Sub test()
Dim qArray() As Long
ReDim qArray(1 To 100)

qArray() = RandomQuestionArray
'loop through your questions

End Sub

Function RandomQuestionArray()  
Dim i As Long, n As Long
Dim numArray(1 To 100) As Long
Dim numCollection As New Collection

With numCollection
    For i = 1 To 100
        .Add i
    Next
    For i = 1 To 100
        n = Rnd * (.Count - 1) + 1
        numArray(i) = numCollection(n)
        .Remove n
    Next
End With

RandomQuestionArray = numArray()

End Function