[RESOLVED] Bubble Sorting an Array?!?!

[rosleenXOXO]

I am trying to sort my array in ascending&Descending order, BUT im having trouble because the code to enter numbers and the code to sort the array was given to me by my professor but i changed the code to enter numbers into the array, so i think that's what messing my code to sort arrays up because the codes aren't matching up....any help is appreciated

Option Strict On

Public Class Form1

    Dim J As Integer = 0
    Dim MyArray As New List(Of Integer)


    Private Sub btnPutNumberIntoArray_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPutNumberIntoArray.Click
        Dim number As Integer
        Integer.TryParse(txtNumbers.Text, number)
        If number < 1 Then
            MessageBox.Show("Please enter a number greater then zero.")
        Else
            MyArray.Add(number)
            txtNumbers.Clear()

        End If
    End Sub

    Private Sub btnDisplayNumbersInArray_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplayNumbersInArray.Click
        txtDisplayNumbers.Clear()
        txtDisplayNumbers.Focus()

        For J As Integer = 0 To MyArray.Count - 1
            txtDisplayNumbers.Text &= MyArray(J).ToString & Environment.NewLine
        Next
    End Sub
Private Sub btnDisplayAscendingOrder_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplayAscendingOrder.Click
     
        Dim SwapFlag As Boolean
        Dim UpperSub As Integer
        Dim Temp As Integer
        UpperSub = 24
        SwapFlag = True

        While SwapFlag = True And UpperSub >= 1
            J = 0
            SwapFlag = False
            While J <= UpperSub - 1
                If MyArray(J) > MyArray(J + 1) Then
                    Temp = MyArray(J)
                    MyArray(J) = MyArray(J + 1)
                    MyArray(J + 1) = Temp
                    SwapFlag = True
                End If
                J = J + 1
            End While

            UpperSub = UpperSub - 1

        End While
            txtDisplayNumbers.Text = txtDisplayNumbers.Text & CStr(MyArray(J)) & ControlChars.NewLine

    End Sub

    Private Sub btnDisplayDescendingOrder_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplayDescendingOrder.Click

        Dim SwapFlag As Boolean
        Dim UpperSub As Integer
        Dim Temp As Integer
        UpperSub = 24
        SwapFlag = True

        While SwapFlag = True And UpperSub <= 1
            J = 0
            SwapFlag = False
            While J >= UpperSub - 1

                If MyArray(J) < MyArray(J + 1) Then
                    Temp = MyArray(J)
                    MyArray(J) = MyArray(J + 1)
                    MyArray(J + 1) = Temp
                    SwapFlag = True
                End If
                J = J + 1
            End While
            UpperSub = UpperSub - 1
            txtDisplayNumbers.Text = txtDisplayNumbers.Text & CStr(MyArray(J)) & ControlChars.NewLine

        End While

    End Sub

At the red Highlight i get this error:
"Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index"

[Evil_Giraffe]

Ho hum, if you don't add enough values in to the List (you're not actually sorting an array, you realise?) you'll get that error. If you add too many values to the List, the end of it won't be sorted.

You've got a hard-coded number of elements that you're trying to sort. But you have a variable length data set that you're sorting. Not happy bed-fellows.

[rosleenXOXO]

Ho hum, if you don't add enough values in to the List (you're not actually sorting an array, you realise?) you'll get that error. If you add too many values to the List, the end of it won't be sorted.

You've got a hard-coded number of elements that you're trying to sort. But you have a variable length data set that you're sorting. Not happy bed-fellows.

Ok im now really confused. What would be enough values if my array can hold 25 elements? so what should i do to fix this? :/

[Evil_Giraffe]

You're not using an array, you're using a List. You add a single value to the List each time you click the btnPutNumberIntoArray button (assuming the number is valid).

The List contains as many elements as you have added. (Unlike an array, which contains as many elements as you size it with)

Therefore, if you have only added 1 element, trying to retrieve the value at position 1 will result in an IndexOutOfRangeException (remember that indices are zero-based, so you only have a position 0)

Add two elements and you have position 0 and 1.
Add a third and you have position 0, 1 and 2.

And so on.

You're trying to retrieve up to position 24 it looks like from a brief code inspection (though I may be suffering from an off-by-one error there), so you need to add 25 values to the list before the code will not throw an IndexOutOfRangeException.

However, if you add more than 25 elements, those additional elements will not be sorted because the code will not try and go beyond position 24 in the List.

[rosleenXOXO]

ok so i changed my code to where it only sorts 5 elements and it works but is there any way i can sort the list so i dont have to worry about how many elements are to be sorted

[Evil_Giraffe]

You already know how to do that. Look at your btnDisplayNumbersInArray_Click_1 sub. That iterates over the (variable) length of the list.

[rosleenXOXO]

would it be MyArray.Count - 1 ?
I tried this it but it still doesnt work :/

  
 Private Sub btnDisplayAscendingOrder_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplayAscendingOrder.Click
        txtDisplayNumbers.Clear()
        txtDisplayNumbers.Focus()
        Dim SwapFlag As Boolean
        Dim UpperSub As Integer
        Dim Temp As Integer
        UpperSub = 4
        SwapFlag = True

        While SwapFlag = True And UpperSub >= 1
            J = 0
            SwapFlag = False
            While J <= UpperSub - 1
                If MyArray.Count - 1 > MyArray.Count Then
                    Temp = MyArray(J)
                    MyArray(J) = MyArray(J + 1)
                    MyArray(J + 1) = Temp
                    SwapFlag = True
                End If
                J = J + 1
            End While

            UpperSub = UpperSub - 1

        End While
        For J As Integer = 0 To MyArray.Count - 1
            txtDisplayNumbers.Text &= MyArray(J).ToString & Environment.NewLine
        Next

[rosleenXOXO]

Also,
How would i make the array in descending order?
i thought all i had to do was flip the ">" sign to the opposite direction from the ascending array code :/

[rosleenXOXO]

NVM on the last question about descending arrays, i figured it out :P
BUTTT i still need help with the previous question

[Shaggy Hiker]

Yeah, that won't work. It kind of looks like you are guessing at solutions rather than thinking them through. Write this down on paper:

Array Slot Value
0 11
1 9
2 13
3 17
4 6
5 8

Once you have that written down, you could add those values into your list (but don't bother, yet, the point is that you COULD add those values, so what you have on paper is what your list would look like if you DID add them in).

How many items are there? That number would be MyArray.Count, and you should see that there are 6 elements with indeces 0-5.

So, if you look at the line you underlined:

If MyArray.Count - 1 > MyArray.Count Then

What does this do? You have already determined that for the example, MyArray.Count = 6, so MyArray.Count -1 = 5. Since 6 is never less than 5, this If statement will ALWAYS be false. That's clearly not what you want to do. But what DO you want to do?

Next, take a look at that demo, and consider what each line of your method will do.

The first line is actually this (ignoring the two lines that clear things):

UpperSub = 4

4??? Why set UpperSub to 4? Where did 4 come from? You mentioned earlier that you got this working for 5 items. Therefore the purpose for the 4 is suggested, since 4 would be the maximum index value in a 5 item list. If we look at the next line this is supported:

While SwapFlag = True And UpperSub >= 1

Clearly, you are looping a certain number of times, and since we later see that UpperSub is being decremented as the last item in the loop, you are counting down from 4 to 1. But your list no longer has four items, it has 6 items. So, would it work if you simply replaced UpperSub = 4 with UpperSub = 6 in the original code? Probably (though I haven't really looked at it), but that would leave you with the same initial problem that EG pointed out: You are hardcoding in the number of elements. What you want is to have the UpperSub, which is your number of iterations, be based on the number of elements in the list. What is that number of elements? It is MyArray.Count. However, you want UpperSub to be not the actual number of elements, but the maximum index, which is MyArray.Count - 1. So set UpperSub = MyArray.Count - 1 in your initial code.

Now you can step through each line in your loop doing the same thing on paper, and see whether or not you get the result you expect. Alternatively, you could set a breakpoint on the While statement, and step through each line of code examining the variables with each step to see whether they are what you expect them to be.

[rosleenXOXO]

NVM i figured it out agian,
thanks for all your help!!!!

[rosleenXOXO]

Yeah, that won't work. It kind of looks like you are guessing at solutions rather than thinking them through. Write this down on paper:

Array Slot Value
0 11
1 9
2 13
3 17
4 6
5 8

Once you have that written down, you could add those values into your list (but don't bother, yet, the point is that you COULD add those values, so what you have on paper is what your list would look like if you DID add them in).

How many items are there? That number would be MyArray.Count, and you should see that there are 6 elements with indeces 0-5.

So, if you look at the line you underlined:

If MyArray.Count - 1 > MyArray.Count Then

What does this do? You have already determined that for the example, MyArray.Count = 6, so MyArray.Count -1 = 5. Since 6 is never less than 5, this If statement will ALWAYS be false. That's clearly not what you want to do. But what DO you want to do?

Next, take a look at that demo, and consider what each line of your method will do.

The first line is actually this (ignoring the two lines that clear things):

UpperSub = 4

4??? Why set UpperSub to 4? Where did 4 come from? You mentioned earlier that you got this working for 5 items. Therefore the purpose for the 4 is suggested, since 4 would be the maximum index value in a 5 item list. If we look at the next line this is supported:

While SwapFlag = True And UpperSub >= 1

Clearly, you are looping a certain number of times, and since we later see that UpperSub is being decremented as the last item in the loop, you are counting down from 4 to 1. But your list no longer has four items, it has 6 items. So, would it work if you simply replaced UpperSub = 4 with UpperSub = 6 in the original code? Probably (though I haven't really looked at it), but that would leave you with the same initial problem that EG pointed out: You are hardcoding in the number of elements. What you want is to have the UpperSub, which is your number of iterations, be based on the number of elements in the list. What is that number of elements? It is MyArray.Count. However, you want UpperSub to be not the actual number of elements, but the maximum index, which is MyArray.Count - 1. So set UpperSub = MyArray.Count - 1 in your initial code.

Now you can step through each line in your loop doing the same thing on paper, and see whether or not you get the result you expect. Alternatively, you could set a breakpoint on the While statement, and step through each line of code examining the variables with each step to see whether they are what you expect them to be.

Yeah, that won't work. It kind of looks like you are guessing at solutions rather than thinking them through.

My professor is horrible, I've had to learn all this all by myself through the internet...
so I am somewhat guessing to find the correct answer. You have been really helpful these couple past days with your responses and i am very grateful. You're probably saving my ass.

[Shaggy Hiker]

My professor is horrible, I've had to learn all this all by myself through the internet...

That is regrettably common.

[Shaggy Hiker]

Let me also refer you to this site for sorting, which Evil_Giraffe told me about:

All the common sorts are there. This one shows the bubble sort, but QuickSort is faster and better, and Shell sort is also of interest.

http://www.youtube.com/watch?v=lyZQP...NSNbAHpPtlfRu3