String Randomizer - vb.net

Question

A friend asked me to make a character string randomizer for a game she plays. I got the code working but now she wants to have the characters seperated every third character with a dash (or a space), but I can't get it to work. Any help will be appreciated.
For x As Integer = 1 To 10
strb.Append(chars(Int(Rnd() * UpperBound)))
If x Mod 2 = 0 Then
strb.Append("-")
The characters need to be separated, but how do I prevent the added dash at the end of the randomized characters?
Thanks guys (and girls) for your help it's working

Answer 1

Just append a dash (or whatever) every third character:
For x As Integer = 1 To 5
strb.Append(chars(Int(Rnd() * UpperBound)))
If x Mod 3 = 0 Then
strb.Append("-")
End If
Next

Answer 2

Since i haven't used those old VB function yet, i'll show you how to do it with VB.NET which could also be converted to C# easily:
Private Function RandomString(rnd As Random, size As Integer) As String
Dim chars() As String = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}
Dim builder As New System.Text.StringBuilder()
For i As Integer = 0 To size - 1
builder.Append(chars(rnd.Next(0, chars.Length)))
Next
Return builder.ToString()
End Function
Let us generate a random string with 5 chars:
Dim rnd = New Random()
Dim rndString = RandomString(rnd, 5)
Note that i'm passing the random instance since. If i would create it in the method and call it in a loop, it would generate the same strings since the Random would use the same time as seed.
Edit: I've only just seen that you need to separate the result. You could use an overloaded version:
Private Overloads Function RandomString(rnd As Random, size As Integer, separator As String, everyNChar As Int32) As String
Dim builder = New System.Text.StringBuilder()
Dim chars() As String = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}
For i As Integer = 0 To size - 1
If i > 0 AndAlso i Mod everyNChar = 0 Then
builder.Append(chars(rnd.Next(0, chars.Length))).Append(separator)
Else
builder.Append(chars(rnd.Next(0, chars.Length)))
End If
Next
Return builder.ToString()
End Function
Note that this will not count the separators.

Answer 3

You can use Regular Expressions to replace strings. It will be simple to change the regex and manage change requests :)
just replace TextBox1.Text = rndstring by :
TextBox1.Text = Regex.Replace(rndstring, "[a-zA-Z0-9]{3}", "$& ")
Note that you need to add Imports System.Text.RegularExpressions if not already done.
EDIT : I have given the above solution to insert a " " (whitespace) after every third character. If you want a hyphen (-) just change the second regex to "$&-"

Answer 4

If I'm understanding you correctly, change the if statement from If x Mod 2 = 0 Then to If x Mod 2 = 0 And x <> 10 Then. That way it wont append the dash if it is on the last element.