計算列表框中的項目總和 - Visual Basic

Question

這是我第一次在這裏發佈。我正在爲我參加的課程制定一些計劃。我需要獲得英里和加侖，然後計算每個條目的MPG。我有這方面的想法。我似乎無法得到的是底部的總數。我需要添加每個ListBox中所有項目的總和，並在每次點擊按鈕時計算總的MPG。這是我的代碼到目前爲止。

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 

在此先感謝您提供的任何幫助。

Answer 1

您的while循環條件不正確，因爲您正在比較ListBox.Items.Count與總數。我會用Linq來代替它，因爲它更具可讀性：

Dim totalMiles As Int32 = milesListBox.Items.Cast(Of Int32)().Sum() 
Dim totalGallons As Int32 = gallonsListBox.Items.Cast(Of Int32)().Sum()