Do ... While problem

Why doesn't the yellow button do what its supposed to do? Is my do, while statement incorrect? The blue and red work. Help! Thank you.

VB Code:

Private Sub BlueButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles BlueButton.Click
        Dim objControl As Control
        For Each objcontrol In Controls
            If TypeOf objcontrol Is Label Then
                objControl.BackColor = BackColor.Blue
            End If
        Next objControl
 
    End Sub
 
    Private Sub YellowButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles YellowButton.Click
        Dim objControl As Control
        Do While TypeOf objControl Is Label
            objControl.BackColor = BackColor.Yellow
        Loop
    End Sub
 
    Private Sub RedButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RedButton.Click
        Dim LabelCollection As New Collection()
        Dim objControl As Control
        For Each objControl In Controls
            If TypeOf objControl Is Label Then
                LabelCollection.Add(objControl)
            End If
        Next objControl
        For Each objControl In LabelCollection
            objControl.BackColor = BackColor.Red
        Next objControl
    End Sub

hi

for (each)...next increments automatically the variable (in your example objControl)

do... loop does NOT increment automatically


for i = 0 to 10
messagebox.show(i)
next

you do not have to increment i


do while i <= 10
messagebox.show(i)
i = i +1
loop

without the statement i = i +1 do...loop will never end because i is not incremented automatically

So then what I have below should work, right? Well it doesn't. It crashes the program when I click on the yellow button.

VB Code:

'runs a loop checking for all labels then changes them to yellow
    Private Sub YellowButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles YellowButton.Click
        Dim objControl As Control
        Dim i As Integer = 1
        Do While i <= 10
            If TypeOf objControl Is Label Then
                objControl.BackColor = BackColor.Yellow
            End If
        Loop
    End Sub

First off objControl will never be a label because it is declared as control and never set to anything else. In the other you make use of the controls collection to assign objControl to a control but here you don't.

VB Code:

Dim objControl As Control 'you are declaring it as a control but it is never set to anything else
        Dim i As Integer = 1
        Do While i <= 10
            If TypeOf objControl Is Label Then
                objControl.BackColor = BackColor.Yellow
            End If
        Loop

I think this is what you mean:

VB Code:

Dim objControl As Control
        For Each objcontrol In Controls
            If TypeOf objcontrol Is Label Then
                objControl.BackColor = BackColor.Yellow
            End If
        Next

Ok, I see what you're saying. I need to use a Do...While...Loop however. How can I do that?

Why do you need to use a Do..While Loop? What is the code suppose to do? If it is just suppose to change all the labels in the controls collection to yellow then a do while loop isn't really what you want to use.

Because that's what the homework is :-D

So how would I use a do while loop to change the backcolor of these labels?

Code:

---

Dim counter As Integer = 0
Do While counter <= Controls.Count - 1
    If TypeOf Controls(counter) Is Label Then
        Controls(counter).BackColor = Color.Yellow
    End If
    counter += 1
Loop

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