Infinite loop when validating input against array - vb.net

Question

The homework task is to simply allow the user to input a value (string) "FD__" and match it against a list of known inputs and return true/false. The ID's are already defined and it works well, when I type an ID which is defined like Products(2) which is "FD3" it will return true, if the value is not defined it will not only give no results but crash the program, so in conclusion true works but false does not. Any information could be helpful.
Design: http://i.imgur.com/bJnFAMX.png
Public Class Form1
'variables
Dim Products(9) As String
Dim Entered As String
Dim Found As Boolean
Public Sub btnFind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnFind.Click
'Product variable array elements
Products(0) = "FD1"
Products(1) = "FD2"
Products(2) = "FD3"
Products(3) = "FD4"
Products(4) = "FD5"
Products(5) = "FD6"
Products(6) = "FD7"
Products(7) = "FD8"
Products(8) = "FD9"
Products(9) = "FD10"
'process
Entered = txtFind.Text 'define entered value as variable
Found = FindNumber() 'sub function
If Found Then
lblResult.Text = Found 'change the results
End If
End Sub
Public Function FindNumber()
'If true statements
Do While (Found = False)
If Entered = Products(0) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(1) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(2) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(3) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(4) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(5) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(6) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(7) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(8) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
ElseIf Entered = Products(9) Then
Found = True
lblResult.ForeColor = Color.LawnGreen
Else 'keeps crashing
Found = False
lblResult.ForeColor = Color.Red
End If
Loop
Return Found
End Function
End Class

Answer 1

You can actually do this with a lot less code... I'm going to go ahead and do some critique while at it.
'1. Functions should have return types
'2. You should pass the function what it needs to do its job
Public Function FindNumber(numberEntered As String) As Boolean
'Rather than evaluating if a condition is true or false, and then returning
'true or false, you can just directly return the condition.
Return Products.Contains(numberEntered)
End Function
Then in your main program:
'This doesn't need to be a class level variable
Dim entered = txtFind.Text
'Local variables should be lowercase
Dim found = FindNumber(entered)
If found Then
'With Option Strict you can't assign a Boolean to a String...
'but you can do .ToString() instead
lblResult.Text = found.ToString()
'And this was really dependent on the result of the function...
'Also it has nothing to do with finding the number...
lblResult.ForeColor = Color.LawnGreen
Else
lblResult.ForeColor = Color.Red
End If
It looks a lot longer, but take out the comments and I promise you it'll be a much simpler (and shorter) program.

Answer 2

You could optimise this whole code by using the .contains function this simple used like this:
if mylist.contains("sometext") then
'change forecolor to green
else
'change forecolor to red
end if
This would mitigate your problem.