Visual Basic If Not Issue - vb.net

Question

I am doing my homework for my visual basic class. I have most of the code written and everything seems to be working well except for my If Not statement that catches the exception when the loop does not find what it is looking for. Anyone see a problem with the way the code looks. The file is loaded in using the browse button already and it works find when I enter information that the loop can find.
Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs)
Handles btnSearch.Click
'event level variables
Dim Found As Boolean
Dim Counter As Integer
'looks for entry match
If rdoAbbrev.Checked = True Then
Do Until Found Or Counter > 257
If Country(Counter).Abbreviation.ToUpper = txtAbbrev.Text.ToUpper Then
Found = True
txtCountry.Text = Country(Counter).Names
Else
Counter += 1
End If
Loop
Else
Do Until Found Or Counter > 257
If Country(Counter).Names.ToUpper = txtCountry.Text.ToUpper Then
Found = True
txtAbbrev.Text = Country(Counter).Abbreviation
Else
Counter += 1
End If
Loop
If Not Found Then
MessageBox.Show("This is not a valid entry.", "NO MATCH FOUND", MessageBoxButtons.OK)
If rdoAbbrev.Checked = True Then
txtAbbrev.Text = ""
txtAbbrev.Focus()
Else
txtCountry.Text = ""
txtCountry.Focus()
End If
End If
End If
'match not found response
'reset variables
Counter = 0
Found = False
End Sub

Answer 1

You If Not Found block only occurs if rdoAbbrev.Checked = True. Is that what you intended? If not, then that block of code should either be located outside of the first If block (below it) or you should have a second If block after the first While loop.
EDIT
It looks like Country is an array. You should probably use Counter >= Country.Length.
Arrays in VB.NET are 0-based. Meaning that the first item is located at Country(0), the second item is at Country(1), etc. If there are 100 elements in the array, then the last element is located at Country(99). Country(100) does not exist and will cause an Exception if you try to access it.
I'm not sure what the requirements of your homework are, but usually to iterate over the elements of a collection (array, list, etc), you would use a For loop. You can jettison from the loop early with the Exit command.
For Counter As Integer = 0 To Country.Length - 1
'...Country(Counter)
If Found Then Exit For
Next

Answer 2

Assuming you want the "Not Found" part to execute regardless of the rdoAbbrev.Checked property, it looks like a slight error in your logic (easily fixed).
Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSearch.Click
'event level variables
Dim Found As Boolean
Dim Counter As Integer
'looks for entry match
If rdoAbbrev.Checked = True Then
Do Until Found Or Counter > 257
If Country(Counter).Abbreviation.ToUpper = txtAbbrev.Text.ToUpper Then
Found = True
txtCountry.Text = Country(Counter).Names
Else
Counter += 1
End If
'You could also write this as:
'Found = Country(Counter).Abbreviation.ToUpper = txtAbbrev.Text.ToUpper
'If Found Then
' txtCountry.Text = Country(Counter).Names
'Else
' Counter += 1
'End If
Loop
Else
Do Until Found Or Counter > 257
If Country(Counter).Names.ToUpper = txtCountry.Text.ToUpper Then
Found = True
txtAbbrev.Text = Country(Counter).Abbreviation
Else
Counter += 1
End If
'You could also write this as:
'Found = Country(Counter).Names.ToUpper = txtCountry.Text.ToUpper
'If Found Then
' txtAbbrev.Text = Country(Counter).Abbreviation
'Else
' Counter += 1
'End If
Loop
End If
'match not found response
'Move your "Not Found" here so that the not found works regardless of the rdoAbbrev.Checked property.
If Not Found Then
MessageBox.Show("This is not a valid entry.", "NO MATCH FOUND", MessageBoxButtons.OK)
If rdoAbbrev.Checked = True Then
txtAbbrev.Text = ""
txtAbbrev.Focus()
Else
txtCountry.Text = ""
txtCountry.Focus()
End If
End If
'reset variables
Counter = 0
Found = False
End Sub

Answer 3

Probably you should End the If statements within their range in the code and avoid ending all your If statements at the end of the code lines. usually works for me in Basic. I think that Basic has a lot of advantages, but for me it still not a high level language that has some problems because it is so easy to work with.