unable to add items to a list in VB.NET - vb.net

Question

Good morning,
so i have received this homework for the summer where i have to create a program to store a list of movies and display them, but the problem is that there isn't a defined number of movie so i can't use the constant method i've always used, so i tried doing that with variables instead, but whenever i press the input button twice the app crashes and i get the error "Index over the matrix limits"
Here's the code in the module
Module Module1
Public Structure Film
Public Titolo As String
Public Autore As String
Public Incasso As Integer
Public Nazionalita As String
End Structure
Public i As Integer = 0
Public Flm(i) As Film
End Module
And here's the input part
Public Class frmInput
Private Sub btnInserisci_Click(sender As Object, e As EventArgs) Handles btnInserisci.Click
If IsNumeric(txtIncasso.Text) = False Then
MsgBox("L'incasso deve essere un valore numerico", MsgBoxStyle.Exclamation, "Attenzione")
ElseIf txtTitolo.Text = "" Or txtAutore.Text = "" Or txtNazionalita.Text = "" Then
MsgBox("Uno o più valori sono vuoti", MsgBoxStyle.Exclamation, "Attenzione")
Else
Flm(i).Titolo = txtTitolo.Text
Flm(i).Autore = txtAutore.Text
Flm(i).Incasso = txtIncasso.Text
Flm(i).Nazionalita = txtNazionalita.Text
i += 1
End If
End Sub
End Class

Answer 1

You should use a List(Of Film) to store the inputs received.
A generic List like that has no practical limits and can grow while you add elements to it
Public Flm As List(Of Film) = new List(Of Film)
....
Else
Dim f as Film = new Film()
f.Titolo = txtTitolo.Text
f.Autore = txtAutore.Text
f.Incasso = txtIncasso.Text
f.Nazionalita = txtNazionalita.Text
Flm.Add(f)
End If
A List(Of Film) could be used like it was an array
For x As Integer = 0 To Flm.Count -1 Step 1
Console.WriteLine("Film #" & x+1)
Console.WriteLine("Titolo = " & Flm(x).Titolo)
.....
Next
And of course you can iterate over it using a simpler foreach
For Each Film f in Flm
Console.WriteLine("Film #" & x+1)
Console.WriteLine("Titolo = " & f.Titolo)
.....
Next

Answer 2

Although others have mentioned using List, which would probably be appropriate, you also mentioned it was a homework task, so maybe you need, or have to, use the more traditional arrays as you have shown. Bearing this in mind, and also to let you know what your problem is. You are incrementing i but not the array.
Public i As Integer = 0
Public Flm(i) As Film
Thus, Flm is 0 to 0, one element.
You add to this, all is OK.
You increment i, good, i += 1
However, you don't then increment the array, Flm(). Incrementing i doesn't automatically increment the array, Flm().
You need to use: ReDim Preserve
Thus... Change:
Else
Flm(i).Titolo = txtTitolo.Text
to:
Else
ReDim Preserve Flm(i)
Flm(i).Titolo = txtTitolo.Text
Lastly, IsNumeric and MsgBox are remnants of the VB6 days, there are vb.net equivalents. Also, using i as a global/public variable is really not good. It's very common, standard, to use i in all local subroutines and functions for little loops etc, it gets used and lost. If you look at almost all examples of code, you'll see i being used as the integer counter.