Bubble Sort logical error VB.NET

This program suppose to sort records(in arySort) in ascending order by last name(index 1 in aryTemp and aryTemp2) and place the result in the list box over the old, preloaded, unsorted records.

It sorts them strangely, I have to click multiple times the Ascending button to get the actual sort result that I suppose to get from clicking the button once.

Why doesn't it sort items with a single mouse click?

The source:

Public Class Form1
    Dim FILE_NAME As String = "Students.txt"
    Dim numberOfRecords As Integer 'total number of records
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If System.IO.File.Exists(FILE_NAME) = True Then
            Dim objReader As New System.IO.StreamReader(FILE_NAME)
            Do While objReader.Peek() <> -1
                lstBox.Items.Add(objReader.ReadLine)
                numberOfRecords += 1
            Loop
            objReader.Close()
        End If
    End Sub

    Private Sub btnAscending_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAscending.Click
        'load all students into array
        Dim arySort(numberOfRecords - 1) As String
        Dim aryTemp() As String 'holds first record's last name
        Dim aryTemp2() As String 'holds second record's last name
        For i = 0 To numberOfRecords - 1
            arySort(i) = lstBox.Items(i)
        Next
        Dim temp As String 'holds temporary record
        Dim k As Integer
        For i = 0 To arySort.Length - 2
            aryTemp = Split(arySort(i), " ")
            For k = i + 1 To arySort.Length - 1
                aryTemp2 = Split(arySort(k), " ")
                If aryTemp(1) < aryTemp2(1) Then
                    temp = arySort(k)
                    arySort(k) = arySort(i)
                    arySort(i) = temp
                End If
            Next
        Next
        lstBox.Items.Clear()
        numberOfRecords = 0
        For i = 0 To arySort.Length - 1
            l开发者_运维技巧stBox.Items.Add(arySort(i))
            numberOfRecords += 1
        Next
    End Sub
End Class

If you just need to sort your list (as you say in the comment), don't implement your own sort mechanism but use the one of .NET:

' Define how we want to compare items '
Function compareByLastName(ByVal item1 As String, ByVal item2 As String) As Integer
    Return String.Compare(item1.Split(" ")(1), item2.Split(" ")(1))
End Function

Private Sub btnAscending_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAscending.Click
    ' load all students into array '
    Dim arySort(numberOfRecords - 1) As String
    For i = 0 To numberOfRecords - 1
        arySort(i) = lstBox.Items(i)
    Next

    ' Use built-in .NET magic '
    Array.Sort(arySort, AddressOf compareByLastName)

    ' Write the values back into your list box '
    lstBox.Items.Clear()
    numberOfRecords = 0
    For i = 0 To arySort.Length - 1
        lstBox.Items.Add(arySort(i))
        numberOfRecords += 1
    Next
End Sub

This uses the built-in quicksort algorithm of the .NET class library. Here's the documentation of the method we are using: Array.Sort(T(), Comparison(Of T)).

compare with my working bubble sort:

Public Sub BubbleSort(ByVal arr() As Integer)
    Dim flag As Boolean = False
    For i As Integer = 0 To arr.Length - 1
        For j As Integer = 0 To arr.Length - 2 - i
            If arr(j + 1) < arr(j) Then
                flag = True
                Dim temp As Integer = arr(j)
                arr(j) = arr(j + 1)
                arr(j + 1) = temp
            End If
        Next
        If flag = False Then Return ' no swaps =>already sorted
    Next
End Sub

I see a two major issues with your algorithm:

• It's not bubble sort. Bubble sort swaps adjacent elements, i.e., it swaps i with i+1. You, on the other hand, swap some element i with the first j > i where name(i) < name(j). Maybe you should show us, in pseudo code, which algorithm you are actually trying to implement?

• aryTemp contains element i and aryTemp2 contains some element j > i. Why do you swap the elements if aryTemp(1) < aryTemp2(1)? Isn't that already the correct order if you want your elements to be sorted ascending?