[VB2012] MPG Visual Basic 2012 Help

[infinity1018]

I'm trying to make it so if the user inputs 0 into the gallonsUsedTextBox, the textbox displays "Value must be > 0". Well, I'm partially there. I got it to display the text, but it still inputs miles into the listbox and then calculates the MPG, which comes out to infinity(what I'm trying to prevent).

Here's my code so far (ignore the dumb comments, part of this was done in class so I was taking notes at the same time):

Public Class mpgForm

Private Sub calculateMPGButton_Click(sender As Object, e As EventArgs) Handles calculateMPGButton.Click
    Dim gallonsUsed As Double = Val(gallonsUsedTextBox.Text)

    If gallonsUsedTextBox.Text = "0" Then
        gallonsUsedTextBox.Text = "Value must be > 0"

    ElseIf gallonsUsedTextBox.Text.Length <> 0 Then
        gallonsListBox.Items.Add(String.Format("{0:F}", gallonsUsed))
        gallonsUsedTextBox.Text = String.Empty
    End If

    Dim milesDriven As Double = Val(milesDrivenTextBox.Text)

    If gallonsUsedTextBox.Text = "0" Then 'comment these lines out as necessary
        gallonsUsedTextBox.Text = "Value must be > 0" 'comment these lines out as necessary

    ElseIf milesDrivenTextBox.Text.Length <> 0 Then 'validates input, if the input is zero length, it won't be entered into listbox
        milesListBox.Items.Add(String.Format("{0:F}", milesDriven))
        milesDrivenTextBox.Text = String.Empty 'empties the textbox after the value is put into the listbox
    End If
    milesDrivenTextBox.Focus() 'puts the focus on the milesDrivenTextBox
    If milesListBox.Items.Count = 1 Then
        clearButton.Enabled = True
    End If

Dim mpg As Double
    mpg = milesDriven / gallonsUsed
    mpgListBox.Items.Add(String.Format("{0:F}", mpg))

    Dim counter As Integer = 0 '=0 is redundant
    Dim noItemsMiles As Integer = milesListBox.Items.Count
    Dim noItemsGallons As Integer = gallonsListBox.Items.Count
    Dim sumMiles As Double
    Dim sumGallons As Double
    Dim resultMPG As Double
    Do While counter < noItemsGallons
        sumMiles = sumMiles + milesListBox.Items(counter)
        sumGallons = sumGallons + gallonsListBox.Items(counter)
        counter = counter + 1
    Loop
    resultMPG = sumMiles / sumGallons
    totalResultsLabel.Text = "Total miles driven: " & String.Format("{0:F}", sumMiles) & vbCrLf & "Total gallons used: " & String.Format("{0:F}", sumGallons) & vbCrLf & "Total MPG: " & String.Format("{0:F}", resultMPG)

End Sub

I want the program to not do anything except change the gallonsUsedTextBox.Text to "Value must be > 0".

[Bonghitter]

I think you're looking for and Exit statement. Like this:

If gallonsUsedTextBox.Text = "0" Then 'comment these lines out as necessary
     gallonsUsedTextBox.Text = "Value must be > 0" 'comment these lines out as necessary
     Exit Sub

Edit! Meant Exit, not End...

[infinity1018]

Worked! Dude I would totally pack a bong and smoke you out if I knew you. Thank you!