Random number/letters

[I'm the doctor.]

Here's the code

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim T() As String = {"A", "A", "B", "C", "D", "E", "E", "F", "G", "H", "I", "I", "J", "J", "K", "L", "M", "N", "O", "O", "P", "Q", "R", "S", "T", "U", "U", "V", "W", "X", "Y", "Z"}
Dim R As Random
Dim nummer As Integer
For i = 1 To 9
R = New Random
nummer = R.Next(0, 32)
Select Case i
Case 1
LblLetter1.Text = T(nummer)
Case 2
LblLetter2.Text = T(nummer)
Case 3
LblLetter3.Text = T(nummer)
Case 4
LblLetter4.Text = T(nummer)
Case 5
LblLetter5.Text = T(nummer)
Case 6
LblLetter6.Text = T(nummer)
Case 7
LblLetter7.Text = T(nummer)
Case 8
LblLetter8.Text = T(nummer)
Case 9
LblLetter9.Text = T(nummer)
End Select
Next
End Sub

When I start my form 9 or atleast 7 of the letters are the same. But when I execute everything step by step then all of the letters are random. Why is that?


------> When I do It step by step.
https://gyazo.com/5c50231ac9d46317057750ae6d89122e
------> When I just execute the program normally
https://gyazo.com/c6cd2cf7827db0af40b3009299d68d88

[Edgemeal]

Your re-initializing the random number generator in the loop, be better to just declare it at the top of the class, I tried like this and only get a few of same chars...

Private R As New Random

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim T() As String = {"A", "A", "B", "C", "D", "E", "E", "F", "G", "H", "I", "I", "J", "J", "K", "L", "M", "N", "O", "O", "P", "Q", "R", "S", "T", "U", "U", "V", "W", "X", "Y", "Z"}
    Dim lbls() = {Label1, Label2, Label3, Label4, Label5, Label6, Label7, Label8, Label9}
    Dim nummer As Integer
    For i = 0 To lbls.Length - 1
        nummer = R.Next(0, T.Length)
        lbls(i).Text = T(nummer)
    Next
End Sub

[I'm the doctor.]

Your re-initializing the random number generator in the loop, be better to just declare it at the top of the class, I tried like this and only get a few of same chars...

Private R As New Random

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim T() As String = {"A", "A", "B", "C", "D", "E", "E", "F", "G", "H", "I", "I", "J", "J", "K", "L", "M", "N", "O", "O", "P", "Q", "R", "S", "T", "U", "U", "V", "W", "X", "Y", "Z"}
    Dim lbls() = {Label1, Label2, Label3, Label4, Label5, Label6, Label7, Label8, Label9}
    Dim nummer As Integer
    For i = 0 To lbls.Length - 1
        nummer = R.Next(0, T.Length)
        lbls(i).Text = T(nummer)
    Next
End Sub

Works like a charm!
Thank you!

[4x2y]

Your re-initializing the random number generator in the loop, be better to just declare it at the top of the class,

This don't explain why run step by step generates random label text!!

After some test i found it is timing problem, when run normal (without break point) R = New Random is execute very fast, so R.Next(0, 32) always start with the same random seed.

To confirm i added Threading.Thread.Sleep(250) at the beginning of the loop then run normally, issue is gone.

[Shaggy Hiker]

Right. The default seed for the random number generator is the system time down to the second. If the loop occurred more than once a second, you would be guaranteed to get the same sequence multiple times. For this reason, it is important to only have one random number generator created per second. The easiest way to guarantee that is to only have one random number generator...period.