15 replies to this topic

[ViRuaL]

This article will teach you how to get random strings for output to a label caption, or anywhere you want it to go.

1. First we need to declare our string names:

Private RndString(2)

This declaration says there will be an array of strings called RndString, and there will be 2 strings in that array.

2. Then, we need to create a function that will generate a random number.

Private Function RandomNumber(rUpper As Integer, Optional rLower As Integer) As Integer

' Generate random number between upper and lower bound values
    Randomize
    RandomNumber = Int((rUpper - rLower + 1) * Rnd + rLower)
End Function

This initializes the Randomize engine, then picks a random number between the upper and lower bound values that you specify.

3. Now we need to define our strings. You'll most likely want them to be defined on form load, but if need be you may put them on a button click or something.

Private Sub Form_Load()
RndString(1) = "Yes"
RndString(2) = "No"
End Sub

This defines our strings for later use.

4. Now let's say you want to change a label's caption when a user clicks a button, to one of the random strings we have previously defined. The code would look something like this:

Command1_Click()
Dim RndNum As Integer
RndNum = RandomNumber(2, 1)
Label1.Caption = RndString(RndNum)
End Sub

This is where the magic happens. RndNum is used to define the index of the string array, and we set it's value equal to a random number, either 2 or 1. Then Label1's Caption becomes the string index of whatever number was produced from the randomize engine.

All done! If you need help with this code or anything else, e-mail me at ViRuaL@gmail.com

[Legend]

Hey thats nice! Well... I was doing it like that:
I was doing a random number, and then I was saying
If RandomNumber = 1 then
String = "Yes"
ElseIf RandomNumber = 2 then
String = "No"
End If

It's easier your way

[turbopowerdmaxsteel]

We can only generate Random numbers within a specified range. However, this number can be used as the index for an array so that we can select a random element from the array, be it an array of Strings, Images, or whatever. What I mean to say is that the process to selecting random picture is the same as that of selecting random strings.

Another thing that I must mention is that this whole stuff we have seen above is not generating a random string, rather selecting a random string. Generating random strings would generate something like zxjhtsjbdjgasd or asdxcbjdkhasd. You can however, select a dictionary word from a list or an array. But, it wouldn't be generating either.

Back to the first question:-

I am assuming you have a collection of wrong answers and a correct answer for each question. (You don't want to make the correct one obvious by filling the wrong ones with those randomly generated strings we just saw, do you?) You need to shuffle the correct answer's position (1, 2, 3 or 4) each time and you need to select 3 wrong answers from the wrong answer collection.

I'll be using the function created by ViRuaL.

STEP 1: First we generate the random position of the correct answer and store it in our variable: Dim CorrectCh As Integer = RandomNumber(1, 4)

STEP 2: Set the correct answer as the text for the appropriate Radio Button: Options(CorrectCh - 1).Text = CorrectAnswer

(Assuming Options to be a zero based array of Radio Buttons)

STEP 3: For each of the remaining positions, generate a random number. Using this number we select a random answer from the list/array of wrong answers and set the text of the Radio Buttons accordingly.

For I As Integer = 1 To 4
	If I = CorrectCh Continue For
	Dim Ch As Integer = RandomNumber(0, WrongAnswers.Length - 1)
	Dim WrongAnswer As String = WrongAnswers(Ch)
	Options(I).Text = WrongAnswer
Next I

Although this code is still not bug free. There's a pretty good chance that the same wrong answer will be repeated. This is because generating a Random Number makes no guarantee that it won't be repeated in the next iteration. To resolve this you can follow either of the ways:-

Method 1

Store the selected answers or their IDs in another array. Whenever a new choice is generated, make sure that this number has not been already generated. If it has been then repeat the process again.

Dim SelectedWrongAnswers As New List(Of Integer)
For I As Integer = 1 To 4
	If I = CorrectCh Continue For
Retry:
	Dim Ch As Integer = RandomNumber(0, WrongAnswers.Length - 1)
	For J as Integer = 0 To SelectedWrongAnswers.Length - 1
		If SelectedWrongAnswers(J) = Ch Then
			Goto Retry
		End If
	Next J
	SelectedWrongAnswers.Add(Ch)
	Dim WrongAnswer As String = WrongAnswers(Ch)
	Options(I).Text = WrongAnswer
Next I

The inner loop can be eliminated by using a HashTable as follows:-

Dim SelectedWrongAnswers As New HashTable
For I As Integer = 1 To 4
	If I = CorrectCh Continue For
Retry:
	Dim Ch As Integer = RandomNumber(0, WrongAnswers.Length - 1)
	If SelectedWrongAnswers(Ch) <> Nothing Then
		Goto Retry
	End If
	Dim WrongAnswer As String = WrongAnswers(Ch)
	SelectedWrongAnswers.Add(Ch, WrongAnswer)
	Options(I).Text = WrongAnswer
Next I

Method 2

This Method is not quite efficient, because the Retry operation may take many iterations if an already generated random number is being generated again. So a better approach is to use a class that generates a non random number. You can find the VB .NET and C# . NET implementation of such a class at http://maxotek.net/blog/?p=9

The following code uses the RandomNumber class declared at http://maxotek.net/blog/?p=9

Dim WrongAnswerGenerator As New RandomNunber(0, WrongAnswers.Length - 1)
For I As Integer = 1 To 4
	If I = CorrectCh Continue For
	Dim Ch As Integer = WrongAnswerGenerator.GetRandomNumber()
	Dim WrongAnswer As String = WrongAnswers(Ch)
	Options(I).Text = WrongAnswer
Next I

[Chesso]

I have not done VB in a long time, but I assume you can make object arrays (filled with strings and what not), or record arrays maybe.

Use that instead of if/then/else if, and if you have something available like record arrays, add an extra value for primary (or the answer), so say if you load 4 strings from file, 1 will be marked in some manner as the correct answer, mark it as primary.

Then if someone checks a box, check the correspendence between radio button and record array, and check it's primary property to see if it's the correct answer.

Anyway, I do all this stuff in Object Pascal (Delphi), but VB should have something.

[turbopowerdmaxsteel]

You need to generate non-repeating Random numbers. I made a class for the same which can generate non-repeating Random numbers within a specified range or select a non-repeating Random number from a supplied list of numbers. The numbers will be repeated after a complete cycle finishes and all the numbers have been generated once.

You can find the VB.NET code at http://maxotek.net/blog/?p=9

You could modify the code a bit to directly select one of your words stored as string types.

Public Class RandomNumber
	Dim WordDomain As New ArrayList	  ' The Words to be generated
	Dim Words As New ArrayList		   ' The Words waiting to be generated
 
	Sub New(ByVal ParamArray Words() As String)
		' Words in a Param Array
		Dim Word As String
		For Each Word In Words
			WordDomain.Add(Word)
		Next
 
		AddItems()
	End Sub

	Sub New(ByVal Words() As String)
		' Words in a String Array
		Dim Word As String
		For Each Word In Words
			WordDomain.Add(Word)
		Next
 
		AddItems()
	End Sub
 
	Private Sub AddItems()
 
		Words.Clear()
		' Insert All Words Into the Array
		Dim I As Integer
		For I = 0 To WordDomain.Count - 1
			Words.Add(WordDomain(I))
		Next
	End Sub
 
	Public Function GetRandomWord() As String
		If Words.Count = 0 Then
			' Re-add the Items, when all the words have been generated.
			AddItems()
		End If
 
		' Return a Random Item and Remove it from the List
		Dim Ch As Integer
 
		' Using Timer as the seed for the Random Number Generation
		Randomize(Microsoft.VisualBasic.Timer)
 
		' Random Number is generated within the range.
		Ch = 0 + CInt(Rnd() * (Words.Count - 1))
 
		Dim Word As String = Words(Ch)
		Words.RemoveAt(Ch)
		Return Word
	End Function
End Class

The above code generates Random words based on a supplied list using a String array or as a ParamArray.