Question

I need to generate a lot of random 2 character strings for my application. it’s a VB console application. basically what I have tried for random strings is this:

  Private Function GenerateRandomString(ByVal intLenghtOfString As Integer) As String
    'Create a new StrinBuilder that would hold the random string.
    Dim randomString As New StringBuilder
    'Create a new instance of the class Random
    Dim randomNumber As Random = New Random
    'Create a variable to hold the generated charater.
    Dim appendedChar As Char
    'Create a loop that would iterate from 0 to the specified value of intLenghtOfString
    For i As Integer = 0 To intLenghtOfString
      'Generate the char and assign it to appendedChar
      appendedChar = Convert.ToChar(Convert.ToInt32(26 * randomNumber.NextDouble()) + 65)
      'Append appendedChar to randomString
      randomString.Append(appendedChar)
    Next
    'Convert randomString to String and return the result.
    Return randomString.ToString()
  End Function

AND THIS:

  Private Function RandomStringGenerator(ByVal intLen As Integer) As String

    Dim r As New Random()

    Dim i As Integer

    Dim strTemp As String = ""

    For i = 0 To intLen

      strTemp = strTemp & Chr(Int((26 * r.NextDouble()) + 65))

    Next

    Return r.Next

  End Function

But when run, it displays something like this:

SR  
SR  
SR  
SR  
SR  
SR  
SR  
SR  
SR  
SR  
BR  
BR  
BR  
BR  
BR  
BR  
BR  
KR  
KR  
KR  
KR

and so on.

What is going on? I thought that I used to, a long time ago, be able to just do random.Next.

Answer 1

I’ve run into similar issues before with the Random object. The problem is that when you instantiate Random it’s default seed value is the number of milliseconds since windows started up. And since you are generating random characters at several a millisecond you end up with the same seed number.

Instead you should create a shared random object instead of instantiating a new one on each call.