Question

这是我第一次在这里发帖。对于我正在上课的课程，我遇到了一些困难。我需要获得里程和加仑然后计算每个条目的MPG。我有这个部分想通了。我似乎无法得到的是底部的总数。我需要在每个ListBox中添加所有项目的总和，并在每次单击按钮时计算总MPG。到目前为止，这是我的代码。

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

提前感谢您提供的任何帮助。

Answer 1

由于您要将while与总和进行比较，因此ListBox.Items.Count循环条件不正确。我会使用Linq代替，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()

计算ListBox- Visual Basic中的项目总和

1 个答案: