vb.net 计算 ListBox 中项目的总和 - Visual Basic
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Calculating the sum of items in a ListBox- Visual Basic
提问by CRunge
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.
这是我第一次在这里发帖。我在我正在上课的课程中遇到了一些困难。我需要获取英里数和加仑数，然后计算每个条目的 MPG。这部分我想通了。我似乎无法得到的是底部的总数。我需要将每个 ListBox 中所有项目的总和相加，并计算每次单击按钮时的总 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
Thanks in advance for any help you can provide.
预先感谢您提供的任何帮助。
回答by Tim Schmelter
Your whileloop conditions are incorrect since you are comparing the ListBox.Items.Countwith the total sum. I would use Linqinstead because it's much more readable:
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()
