AI for Tic Tac Toe

VB Code:

Public Function compturn()
 
'
 
Dim compmove As Integer
Dim mask As Object
mask = Format(compmove, "btn#")
compmove = CStr(Int(Rnd() * 10))
Label4.Text = mask
mask.Text = "O"
mask.Enabled = False
 
'Make sure that a button that is already clicked
'by either the user or the computer is not clicked again
 
If mask.Enabled = False And compmove = 1 Then
compmove += 1
 
If compmove = 10 Then
compmove = 1
End If
End If

So I have my form settup with 9 buttons named btn1, btn2...etc
I'm trying to make it so that if you click a button it will go X, then the computer will randomly select a spot, the problem lies in this line "mask.Text = "O" " or at least that is where the error is given, any help or suggestions would be greatly appreciated, I can try to explain more of what i'm trying to do but I need specific questions otherwise i dont know what to tell you.. thanks in advance

http://planet-source-code.com

Check in VB and you will see a lot of exemple. This game was created more than once in the past :)

this is VB.net, but i'll check still any help would be appreciated

I know that's vb.net but the AI doesn't change. I'll send you a piece of code if I can get back my old tictacttoe project.

anyone have any good tutorial sites, it doesnt have to relate to this, just tutorials on anything and everything from beginner to advanced?