VB displaying elements from multidimensional array in listbox - arrays

Question

For some odd reason I am getting an error when I am using my loop to display the elements of my array. I can't seem to understand what it is I am doing or not doing right. This is the code so far. This is not for a class, I am learning myself.
Option Strict On
Option Explicit On
Option Infer Off
Public Class Form1
Private strExams(49, 2) As String
Dim count As Integer = 0
Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
Dim strStudent As String = txtStudent.Text
Dim strTest As String = txtTest.Text
Dim strScore As String = txtScore.Text
If count <= 49 Then
strExams(count, 0) = strStudent
strExams(count, 1) = strTest
strExams(count, 2) = strScore
count += 1
End If
txtStudent.Text = String.Empty
txtTest.Text = String.Empty
txtScore.Text = String.Empty
txtStudent.Focus()
End Sub
Private Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click
Dim intHighRow As Integer = strExams.GetUpperBound(0)
Dim intHighCol As Integer = strExams.GetUpperBound(1)
Dim intR As Integer
Dim intC As Integer
Do While intC <= intHighCol
intR = 0
Do While intR <= intHighRow
lstMessage.Items.Add(strExams(intR, intC))
intR += 1
Loop
intC += 1
Loop
End Sub
This is the error I am getting when I click my display button.
An unhandled exception of type 'System.ArgumentNullException' occurred in System.Windows.Forms.dll
Additional information: Value cannot be null.

Answer 1

Try this. This makes much more sense to me. The reason you're getting a null error is that you haven't filled everything up in your array and your listbox can't list null items. So a workaround would be to enumerate only items that already have values, thus, just loop until the last value of count.
Private Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click
Dim intR As Integer
lstMessage.Items.Clear()
Do While intR < count
lstMessage.Items.Add(strExams(intR, 0) & " - " & strExams(intR, 1) & " - " & strExams(intR, 2))
intR += 1
Loop
End Sub