vb.net generate random number and string - vb.net

Question

I want to generate a random number of 6 intergers in vb.net which should be number and also some times alphanumerice.Like ist 4 or 5 numbers should be numbers and next should be alphnumeric.I created both numbers separatedly.like this
Public Function rand() As String
'Number
Dim rng As Random = New Random
Dim number As Integer = rng.Next(1, 1000000)
Dim digits As String = number.ToString("000000")
'Alphnumeric
Dim s As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
Dim r As New Random
Dim sb As New StringBuilder
For i As Integer = 1 To 5
Dim idx As Integer = r.Next(0, 35)
sb.Append(s.Substring(idx, 1))
Next
End Function
Now Any One Give Me Idea that in this function can i return number and some times string or may b a single instances which create both numbers and strings.

Answer 1

The first problem to solve is the random number generator. You should use only one instance and not multiple instances that gives back the same sequence if called in short time distance. Then it is
difficult to say what 'something' means in your requirements, but supposing you are fine with rougly 70% numbers and 30% a mix of numbers and strings then you call the random generator to decide for a sequence of only numbers or a mixed one. Based on the output of the random selection of the sequence build from the appropriate string
' A global unique random generator'
Dim rng As Random = New Random
Sub Main
Console.WriteLine(rand())
Console.WriteLine(rand())
Console.WriteLine(rand())
Console.WriteLine(rand())
End Sub
Public Function rand() As String
Dim sb As New StringBuilder
' Selection of pure numbers sequence or mixed one
Dim pureNumbers = rng.Next(1,11)
if pureNumbers < 7 then
' Generate a sequence of only digits
Dim number As Integer = rng.Next(1, 1000000)
Dim digits As String = number.ToString("000000")
For i As Integer = 1 To 6
Dim idx As Integer = rng.Next(0, digits.Length)
sb.Append(digits.Substring(idx, 1))
Next
else
' Generate a sequence of digits and letters
Dim s As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
For i As Integer = 1 To 6
Dim idx As Integer = rng.Next(0, 36)
sb.Append(s.Substring(idx, 1))
Next
End if
return sb.ToString()
End Function