Question

Have to pick a random number from an arraylist, to generate proper information from a database, its bugging on the rnd line at this moment

    Dim rn As New List(Of Integer)
    Dim QPass As String
    rn.Add(71)
    rn.Add(72)
    rn.Add(79)
    rn.Add(80)
    Dim index As Integer = CInt(Math.Floor(Rnd() * 4))
    Dim randomValue As Integer = CInt(rn(index))
    QPass = randomValue.ToString()
    Session("Pt2") = rn
    PT2imgImage.ImageUrl = "showImage.ashx?i=" + QPass
    PT2imgImage.Width = Unit.Pixel(600)

Answer 1

Here

rn = rn(Rnd() * 4)

you are trying to put an Integer (the value selected from the ArrayList), into a variable declared as ArrayList. That won’t work. Use a new variable:

Dim index As Integer = CInt(Math.Floor(Rnd() * 4))
Dim randomValue As Integer = CInt(rn(index))

QPass = randomValue.ToString()
Session("Pt2") = randomValue

CInt(Math.Floor(...)) ensures that the floating point value returned from Rnd() * 4 is correctly rounded down and converted into an integer, which can then be used to index an array list. Eventually, you might want to replace this by a more .NET way to get a random number (e.g. Random.Next). Rnd is mainly for backwards compatibility.

The CInt around rn(index) is required, since you use an old, untyped ArrayList instead of a new, shiny, strongly-typed List(Of Integer). If you use the latter, you can remove the outer CInt.