Visual Basic- random number

Question

I have some VB code that gives me a random number, 1 between 20 (X). However, within 20 attempts, I will get the same number twice. How can I get a sequence of random numbers without any of them repeating? I basically want 1-20 to show up up in a random order if I click a button 20 times.

    Randomize()
    ' Gen random value

    value = CInt(Int((X.Count * Rnd())))

    If value = OldValue Then
        Do While value = OldValue
            value = CInt(Int((X.Count * Rnd())))    
        Loop
    End If

possible duplicate of Write a method to shuffle a deck of cards in VB.NET — Hans Passant
– Hans Passant, Commented Mar 28, 2013 at 4:25

djv · Accepted Answer · 2013-03-28 04:14:10Z

1

For 1 to 20, use a data structure like a LinkedList which holds numbers 1 to 20. Choose an index from 1 to 20 at random, take the number at that index, then pop out the number in that location of the LinkedList. Each successive iteration will choose an index from 1 to 19, pop, then 1 to 18, pop, etc. until you are left with index 1 to 1 and the last item is the last random number. Sorry for no code but you should get it.

answered Mar 28, 2013 at 4:14

djv

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Rajaprabhu Aravindasamy · Accepted Answer · 2013-03-28 05:48:05Z

1

The concept is, you have to add the generated random number into a list, and before adding it into the list, make sure that the new number is not contains in it. Try this code,

        Dim xGenerator As System.Random = New System.Random()
        Dim xTemp As Integer = 0
        Dim xRndNo As New List(Of Integer)

        While Not xRndNo.Count = 20

            xTemp = xGenerator.Next(1, 21)

            If xRndNo.Contains(xTemp) Then
                Continue While
            Else
                xRndNo.Add(xTemp)
            End If

        End While

[Note: Tested with IDE]

answered Mar 28, 2013 at 5:48

Rajaprabhu Aravindasamy

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Zeeshan · Accepted Answer · 2013-03-28 04:01:35Z

0

for that purpose, you need to store all previous generated number, not just one, as u did in OldValue named variable. so, store all previously generated numbers somewhere (list). and compare the newly generated number with all those in list, inside ur while loop, and keep generating numbers, while number is not equal to any of one in list..

answered Mar 28, 2013 at 4:01

Zeeshan

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dbasnett · Accepted Answer · 2013-03-28 15:12:12Z

0

Add the numbers to a list and then pick them in a random order, deleting them as they are picked.

Dim prng As New Random
Dim randno As New List(Of Integer)

Private Sub Button1_Click(sender As Object, _
                          e As EventArgs) Handles Button1.Click
    If randno.Count = 0 Then
        Debug.WriteLine("new")
        randno = Enumerable.Range(1, 20).ToList 'add 1 to 20 to list
    End If
    Dim idx As Integer = prng.Next(0, randno.Count) 'pick a number
    Debug.WriteLine(randno(idx)) 'show it
    randno.RemoveAt(idx) 'remove it
End Sub

answered Mar 28, 2013 at 15:12

dbasnett

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