IndexOutOfRangeException was Unhandled. Cannot find table 0 - vb.net

Question

can anyone please help on how to fix this error? im getting an error "Error:Syntax error(missing operator)in query expression '''ans'." this is my code:
Imports System.Data
Imports System.Data.OleDb
Public Class frmExam : Inherits System.Windows.Forms.Form
Dim ds As New DataSet()
Dim qno() As Integer
Dim pos As Integer
Private Sub btnFinish_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFinish.Click
ProcessAnswer()
Dim i, marks As Integer
Dim dr As DataRow
marks = 0
For i = 0 To NOQ - 1
dr = ds.Tables(0).Rows(qno(i))
If Not IsDBNull(dr.Item("ans")) AndAlso dr.Item("CorrectAns") = dr.Item("ans") Then
marks += 1
End If
Next
Try
con.Open()
Dim cmd As New OleDbCommand("insert into stud values(stud.nextval,'" & SubjectCode & "','" & Username & "','" & marks & ")", con)
MsgBox(cmd.CommandText)
cmd.ExecuteNonQuery()
Dim msg As String
msg = "UserName : " & Username & ControlChars.CrLf & _
"Subject : " & SubjectCode & ControlChars.CrLf & _
"Total Questions : " & NOQ & ControlChars.CrLf & _
"Marks : " & marks
MsgBox(msg, "Result")
Catch ex As Exception
MsgBox(ex.Message)
Finally
If con.State <> ConnectionState.Closed Then
con.Close()
End If
End Try
Me.Dispose()
End Sub
Private Sub frmExam_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ReDim qno(NOQ)
Try
Dim da As New OleDbDataAdapter("select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' ans from question where SubjectCode = " & SubjectCode, con)
da.Fill(ds, "question")
Catch ex As Exception
MsgBox("Error:" & ex.Message)
Me.Dispose()
End Try
Randomize()
Dim totrows As Integer
totrows = ds.Tables(0).Rows.Count
Dim i, r, j As Integer
Dim present As Boolean
i = 0
Do While i < 5
r = CInt((totrows - 1) * Rnd())
present = False
For j = 0 To i
If r = qno(j) Then
present = True
Exit For
End If
Next
If Not present Then
qno(i) = r
i = i + 1
End If
Loop
pos = 0
DisplayQuestion()
End Sub
Sub DisplayQuestion()
Dim row As DataRow
lblQno.Text = Str(pos + 1) & "/" & NOQ
lblSubcode.Text = "Subject : " & SubjectCode
row = ds.Tables(0).Rows(qno(pos))
txtQuestion.Text = row.Item(0)
txtAns1.Text = row.Item(1)
txtAns2.Text = row.Item(2)
txtAns3.Text = row.Item(3)
txtAns4.Text = row.Item(4)
lblQNo2.Text = Str(pos + 1) & "/" & NOQ
lblSubCode2.Text = "Subject:" & SubjectCode
row = ds.Tables(0).Rows(qno(pos))
txtQuestion2.Text = row.Item(0)
txtAnsTrue.Text = row.Item(1)
txtAnsFalse.Text = row.Item(2)
lblQNo3.Text = Str(pos + 1) & "/" & NOQ
lblSubcode.Text = "Subject : " & SubjectCode
row = ds.Tables(0).Rows(qno(pos))
txtQuestion3.Text = row.Item(1)
txtAns.Text = row.Item(2)
End Sub
Private Sub btnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext.Click
ProcessAnswer()
If pos < NOQ - 1 Then
pos = pos + 1
DisplayQuestion()
Else
Beep()
End If
End Sub
Private Sub btnPrev_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev.Click
ProcessAnswer()
If pos > 0 Then
pos = pos - 1
DisplayQuestion()
End If
End Sub
Public Sub ProcessAnswer()
Dim row As DataRow
Dim ans As String = ""
row = ds.Tables(0).Rows(qno(pos))
If rdbtnAns1.Checked Then
ans = "1"
End If
If rdbtnAns2.Checked Then
ans = "2"
End If
If rdbtnAns3.Checked Then
ans = "3"
End If
If rdbtnAns4.Checked Then
ans = "4"
End If
If rdbtnTrue.Checked Then
ans = "1"
End If
If rdbtnFalse.Checked Then
ans = "2"
End If
If txtAns.Text = "" Then
ans = "txtAns"
End If
ds.Tables(0).Rows(qno(pos)).Item("Ans1") = ans
End Sub
Private Sub btnPrev2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev2.Click
ProcessAnswer()
If pos > 0 Then
pos = pos - 1
DisplayQuestion()
End If
End Sub
Private Sub btnNext2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext2.Click
ProcessAnswer()
If pos < NOQ - 1 Then
pos = pos + 1
DisplayQuestion()
Else
Beep()
End If
End Sub
Private Sub btnPrev3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrev3.Click
ProcessAnswer()
If pos > 0 Then
pos = pos - 1
DisplayQuestion()
End If
End Sub
Private Sub btnNext3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext3.Click
ProcessAnswer()
If pos < NOQ - 1 Then
pos = pos + 1
DisplayQuestion()
Else
Beep()
End If
End Sub
End Class
this is the highlighted texxt:totrows = ds.Tables(0).Rows.Count

Answer 1

When you want to use an alias for a field expression, Access requires you to use the AS keyword.
This would fail ...
select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' ans from question
This could work ...
select Question, Ans1, Ans2, Ans3, Ans4, CorrectAns, QType, '' AS ans from question
However, I would be uneasy with a field whose name matched the table name. If you can't rename that field, alias the table, and qualify the fields with the table alias.
select q.Question, q.Ans1, q.Ans2, q.Ans3, q.Ans4, q.CorrectAns, q.QType, '' AS ans from question AS q