Example capx, made in last beta r249
The interest of arrays in the OP's question is to allow to pick out of the cards the user do not own, which your method does not display dop2000.
gorillakelvin, like in JS, arrays in Construct are zero-based, and the index starts from zero.
On start of layout I manually set some informations, like you did, and then in the following sub-event, I loop through aUserOwn and dynamically modify aUserNoOwn size so it contains only the "Not own cards".
Then, when you click the button, you randomly pick a number from the array aUserNoOwn and display it in the textbox.
Since we are zero based, expected answers are actually 0,2,4,6,8.