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this is my first time posting on here. I'm having some difficulty with a program for a class I'm taking. I need to get the miles and gallons then calculate the MPG for each entry. I have this part figured out. What I can't seem to get is the totals at the bottom. I need to add the sum of all the items in each ListBox and calculate the total MPG each time the button is clicked. Here's my code so far.

Public Class MilesPerGallon
    Private Sub calculateMPGButton_Click(sender As System.Object,
        ByVal e As System.EventArgs) Handles calculateMPGButton.Click

        Dim miles As Double ' miles driven
        Dim gallons As Double ' gallons used
        Dim totalMiles As Double ' total miles driven
        Dim totalGallons As Double ' total gallons used
        Dim counter As Integer

        miles = milesDrivenTextBox.Text ' get the miles driven
        gallons = gallonsUsedTextBox.Text ' get the gallons used

        If milesDrivenTextBox.Text <> String.Empty Then
            ' add miles to the end of the milesListBox
            milesListBox.Items.Add(milesDrivenTextBox.Text)
            milesDrivenTextBox.Clear() ' clears the milesDrivenTextBox
        End If

        If gallonsUsedTextBox.Text = 0 Then
            ' do not divide by 0 and alert 0
            gallonsUsedTextBox.Text = "Cannot equal 0"
        End If

        If gallonsUsedTextBox.Text > 0 Then
            ' add gallons to the end of the gallonsListBox
            gallonsListBox.Items.Add(gallonsUsedTextBox.Text)
            mpgListBox.Items.Add(String.Format("{0:F}", miles / gallons))
            gallonsUsedTextBox.Clear() ' clears the gallonsUsedTextBox
        End If

        totalMiles = 0
        totalGallons = 0
        counter = 0

        Do While totalMiles < milesListBox.Items.Count
            miles = milesListBox.Items(totalMiles)
            totalMiles += miles
            counter += 1

            Do While totalGallons < gallonsListBox.Items.Count
                gallons = gallonsListBox.Items(totalGallons)
                totalGallons += gallons
                counter += 1
            Loop
        Loop
        If totalMiles <> 0 Then


            totalResultsLabel.Text = "Total miles driven: " & totalMiles & vbCrLf &
                "Total gallons used: " & totalGallons & vbCrLf & "Total MPG: " &
                String.Format("{0:F}", totalMiles / totalGallons)
        End If
    End Sub
End Class

Thanks in advance for any help you can provide.

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1 回答 1

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您的while循环条件不正确，因为您将ListBox.Items.Count与总和进行比较。我会改用Linq它，因为它更具可读性：

Dim totalMiles As Int32 = milesListBox.Items.Cast(Of Int32)().Sum()
Dim totalGallons As Int32 = gallonsListBox.Items.Cast(Of Int32)().Sum()
于 2013-06-24T21:42:06.337 回答