Generating Three Unique Random Numbers in Visual Basic? - vb.net

Question

I have been working on an app lately that displays three random photos. The form consists of three pictureboxes and a button. When the user clicks a button, three different images are shown. The problem is, however, these three images are not always unique, most of the time there will be doubles and often triples too. I tried to implement a function to catch this but all it succeeded at was lowering the chances of identical images. There are over 50 images to choose from, so it's not like there isn't enough. Here is the code for the failed solution I came up with:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
RandomImageOne()
RandomImageTwo()
RandomImageThree()
If imagenumber1.Text or imagenumber2.Text = imagenumber3.Text Then
RandomImageThree()
End If
If imagenumber1.Text or imagenumber3.Text = imagenumber2.Text Then
RandomImageTwo()
End If
If imagenumber3.Text or imagenumber2.Text = imagenumber1.Text Then
RandomImageOne()
End If
End Sub
The 'RandomImage' functions generate a random number in a label (eg. imagenumber1), these numbers correlate with the number of one of the 50 images. I realize that this is probably not the smartest method, but I am not familiar with any other way.
I need to be able to either generate three unique numbers, so that I don't have to worry about programming in something to stop double and triple images, or create a solution that works 100% of the time to catch the double or triple images.
Any help would be very much appreciated, especially if it were explained simply. Thank you.

Answer 1

I would generate random image 1 and image 2, testing that image 2 is distinct using a while loop. Only once that that is done would I then move on to generating image three.
Information on the while loop is here.
So in rough code (it's been a while since I used VBA properly):
RandomImageOne()
RandomImageTwo()
do while imagenumber1.text = imagenumber2.text
RandomImageTwo()
loop
RandomImageThree()
do while imagenumber3.text = imagenumber2.text or imagenumber3.text = imagenumber1.text
RandomImageThree()
loop

Answer 2

It might not be the most efficient way but it works...
First create a function that returns a list of three items:
Public Function ProvideUniqueNumbers(NoList As List(Of Integer), _
HowManyToReturn As Integer) As List(Of Integer)
Dim Generator As System.Random = New System.Random()
Dim n As Integer = NoList.Count
Dim index As Integer = Generator.Next(1, n)
Dim ReturnList As List(Of Integer) = New List(Of Integer)
For i = 1 To HowManyToReturn
n = NoList.Count
index = Generator.Next(1, n)
ReturnList.Add(NoList(index))
NoList.RemoveAt(index)
'NoList.Dump()
Next
Return ReturnList
End Function
Then create a list of integers for your collection. For instance:
List(Of Integer) MyList = New List(Of Integer)
For i As Integer = 0 To YourImageArray.Count - 1
MyList.Add(i)
Next
Finally Call the function and distribute the results:
Dim result As List(Of Integer) = ProvideUniqueNumbers(MyList,3)
image1 = YourImageArray(result(0))
image2 = YourImageArray(result(1))
image3 = YourImageArray(result(2))

Answer 3

This isn't a solution but a note.
This doesn't do what you think it does
If imagenumber1.Text or imagenumber2.Text = imagenumber3.Text Then
RandomImageThree()
End If
You have to compare each element
If imagenumber1.Text = imagenumber3.Text or imagenumber2.Text = imagenumber3.Text Then
RandomImageThree()
End If