Click here to Skip to main content
Rate this: bad
good
Please Sign up or sign in to vote.
See more: VB.NET
Hey all,
 
I've been wondering about generating random numbers within a certain range for a while.
Recently I've been using something like this a lot:
Dim Generator As New Random
Generator.Next(1, 30)
(this generates numbers ranging from 1 up to and including 29)
 
In the past I was told to use Rnd and that I needed to call Randomize first, but because I can easily generate a random number within a range with Random I've been using that. It was long ago that I used Rnd and Randomize.
 
What I'm trying to do is something like this:
I want to shuffle 2 decks of cards as I load a form.
To shuffle one deck I do this:
            Dim DeckBefore As New Collection
            Dim DeckAfter As New Collection
            Dim Position As New Random
            Dim ChosenCard As Integer
 
            While DeckBefore.Count > 0
                ChosenCard = Position.Next(1, DeckBefore.Count + 1)
                DeckAfter.Add(DeckBefore.Item(ChosenCard))
                DeckBefore.Remove(ChosenCard)
            End While
Imagine DeckBefore to be a list of cards like this: Ace of Spaces, Two of Spades, Three of Spades .. and so on
DeckAfter could be something like this: Jack of Hearts, Seven of Clubs, Three of Diamonds, King of Spades .. and so on
 
The problem I encounter is that if I use this code for 2 separate decks, they end up identically (although not the same each time). I understand this has to do with the seed value of the Random, and that is automatically picks the date/time for a seed value if I don't give it one.
 
All I want really is for my program to order cards "randomly" each time so that a player won't be able to predict (out of the top of his/her head) what card comes next.
 
any help would be appreciated.
Posted 7-Jan-13 17:33pm
Rate this: bad
good
Please Sign up or sign in to vote.

Solution 2

Don't declare the Random object in the method. Try declaring it once at the class level.
  Permalink  
Comments
OneInNineMillion at 8-Jan-13 0:19am
   
Is this because my program will eventually use more memory if I keep declaring new variables and objects each time (for example) I call a function?
Dave Kreskowiak at 8-Jan-13 0:23am
   
No, it has nothing to do with that. It's simply to do with how Random works. If the method this code is in is called twice, in quick succession, it's possible that the two Random objects that are created will be created with the same seed value from the system timer, thereby giving you the same string of numbers.
Sergey Alexandrovich Kryukov at 8-Jan-13 0:24am
   
Agree, a 5.
—SA
OneInNineMillion at 8-Jan-13 0:33am
   
Awesome, that solved my problem. Thanks for explaining too.
Rate this: bad
good
Please Sign up or sign in to vote.

Solution 1

You can choose a seed of your own devising if you like, but there is no such thing as a random sequence on a computer. I think you're still safe, this is about all that any card program probably does.
  Permalink  
Comments
OneInNineMillion at 8-Jan-13 0:18am
   
I'm not to worried about the "random sequence" not really being random. The only thing that bothers me really is that I get two identically shuffled decks of cards. I was wondering if there was an easy way to make sure the two decks end up being shuffled differently from each other. Maybe by taking the default time as a seed for one sequence and the time + 1 as a seed for the other.
Christian Graus at 8-Jan-13 1:08am
   
Yes, if you shuffle two decks at once, you need two different seeds. I suggest just taking xx minutes off DateTime.Now.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)



Advertise | Privacy | Mobile
Web02 | 2.8.141022.2 | Last Updated 8 Jan 2013
Copyright © CodeProject, 1999-2014
All Rights Reserved. Terms of Service
Layout: fixed | fluid

CodeProject, 503-250 Ferrand Drive Toronto Ontario, M3C 3G8 Canada +1 416-849-8900 x 100