Confused about Arrays in VB.net - arrays

Question

I'm working on a project for college in which I have to create a program which stored twenty questions and answers entered on a teachers form which are then displayed one after the other (after clicking the next button) on a student form.
the issue I'm having is that I can enter the questions and answers ( array 0 to 19) however when the students are answering the questions only 19 are shown with the last question not appearing.
Let me know what I can show you to help solve my issue.
Module Module1
Public myQ(0 To 19) As String
Public myA(0 To 19) As String
End Module
Public Class frmTeacher
Public myCounter As Integer
Private Sub frmTeacher_Load(sender As Object, e As EventArgs) Handles MyBase.Load
myCounter = (0)
End Sub
Private Sub btnTeacherNext_Click(sender As Object, e As EventArgs) Handles btnTeacherNext.Click
If myCounter < 19 Then
myQ(myCounter) = txtTeacherQ.Text
myA(myCounter) = txtTeacherA.Text
myCounter = myCounter + 1
txtTeacherQ.Text = ""
txtTeacherA.Text = ""
Else
MsgBox("20 Questions Created, Moving on To Student Screen")
Me.Hide()
frmStudent1.Show()
End If
End Sub
Public Class frmStudent1
Dim myScore As Integer
Dim MyCounter2 As Integer
Public myNames As String
Private Sub btnStudentHelp_Click(sender As Object, e As EventArgs) Handles btnStudentHelp.Click
MsgBox("Questions will be shown to the left, Place your answer into the box on the right and click next")
End Sub
Private Sub frmStudent1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
lblStudentQ.Text = myQ(0)
HideItAll()
txtStudentName.Visible = True
btnStart.Visible = True
End Sub
Private Sub HideItAll()
lblStudentQ.Visible = False
txtStudentA.Visible = False
txtStudentName.Visible = False
btnStudentHelp.Visible = False
btnNextStudent.Visible = False
btnStart.Visible = False
btnStudentNext.Visible = False
End Sub
Private Sub btnStudentNext_Click(sender As Object, e As EventArgs) Handles btnStudentNext.Click
If MyCounter2 < 19 Then
If txtStudentA.Text = myA(MyCounter2) Then
myScore = myScore + 1
End If
MyCounter2 = MyCounter2 + 1
lblStudentQ.Text = myQ(MyCounter2)
Else
MsgBox("Your score is " + Str(myScore))
myNames = myNames + txtStudentName.Text + ": " + Str(myScore) + vbNewLine
HideItAll()
btnNextStudent.Visible = True
End If
End Sub
Private Sub btnNextStudent_Click(sender As Object, e As EventArgs) Handles btnNextStudent.Click
Me.Refresh()
HideItAll()
txtStudentName.Visible = True
btnStart.Visible = True
End Sub
Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
myScore = 0
MyCounter2 = 0
If txtStudentName.Text = "teacher" Then
MsgBox("The scores are as follows: " + vbNewLine + myNames)
End If
HideItAll()
lblStudentQ.Visible = True
txtStudentA.Visible = True
btnStudentHelp.Visible = True
btnStudentNext.Visible = True
End Sub
End Class

Answer 1

change this:
If MyCounter2 < 19 Then
to:
If MyCounter2 < 20 Then
or:
If MyCounter2 <= 19 Then

Answer 2

When you declare your arrays as
Public myQ(0 To 19) As String
you have effectively created an array that could hosts 20 strings and their indexes are from 0 to 19 max. This means that your myCounter2 variable could have as maximum value 19 otherwise you go out of bound of the array. At the same time if you show only the questions and answers that have an index less that 19 you loose the last couple of question/answer
You should fix your code using this kind of conditional
If MyCounter2 < myQ.Length Then
.....
Array.Length returns the number of elements that could be stored in all the dimensions of the array (20).
Using this property is better because, if you change the array size (say you want to ask 40 questions getting 40 answers) then you don't need to check every line of your code to adjust magic numbers appearing everywhere.
But, after the change, this line of the btnStudentNext_Clicks event fails when MyCounter2 value is 19
' MyCounter2 = 19 + 1
MyCounter2 = MyCounter2 + 1
' this fails because at this point MyCounter2 is 20
lblStudentQ.Text = myQ(MyCounter2)
A possible refactoring of your code could be
Private Sub btnStudentNext_Click(sender As Object, e As EventArgs) Handles btnStudentNext.Click
If MyCounter2 < myQ.Length Then
If txtStudentA.Text = myA(MyCounter2) Then
myScore = myScore + 1
End If
MyCounter2 = MyCounter2 + 1
End if
if MyCounter2 >= myQ.Length Then
ShowResults();
else
lblStudentQ.Text = myQ(MyCounter2)
txtStudentA.Text = ""
Endif
End Sub
Private Sub ShowResults()
MsgBox("Your score is " + Str(myScore))
myNames = myNames + txtStudentName.Text + ": " + Str(myScore) + vbNewLine
HideItAll()
btnNextStudent.Visible = True
End Sub