[RESOLVED] Ordering a row of picturebox by colour using merge sort

[Furqan Raheem]

I'm making a snakes game . Every time the snake eats, a new picturebox is created with a random colour. I'm trying to sort the order of the pictureboxes by colour using merge sort by using the pictureboxes' assigned tabindex. And I've only included the relevant subroutines as the whole program is rather big.

I've coded in the merge sort subroutine but get caught with an error.I get an "index is out of bounds" error.

Public class game

Dim snake(1000) as picture box
Dim DataStore() As Integer
Dim TempStore() As Integer
Private Sub MergeSort(ByVal ptrFirst As Integer, ByVal ptrLast As Integer)
    Dim ptrMiddle As Integer

    If (ptrLast > ptrFirst) Then
        ptrMiddle = (ptrFirst + ptrLast) \ 2
        MergeSort(ptrFirst, ptrMiddle)
        MergeSort(ptrMiddle + 1, ptrLast)
        Merge(ptrFirst, ptrMiddle, ptrLast)
    End If

End Sub

Private Sub Merge(ByVal beginning As Integer, ByVal ptrMiddle As Integer, ByVal ending As Integer)
    ReDim TempStore(snake(body).TabIndex)
    Dim CountLeft As Integer
    Dim CountRight As Integer
    Dim counterMain As Integer

    For counter = 0 To body
        TempStore(counter) = DataStore(counter)
    Next
    CountLeft = beginning
    CountRight = ptrMiddle + 1
    counterMain = beginning

    Do While (CountLeft <= ptrMiddle) And (CountRight <= ending)

        If (TempStore(CountLeft) <= TempStore(CountRight)) Then
            DataStore(counterMain) = TempStore(CountLeft)
            CountLeft = CountLeft + 1
        Else
            DataStore(counterMain) = TempStore(CountRight)
            CountRight = CountRight + 1
        End If
        counterMain = counterMain + 1
    Loop
    If CountLeft <= ptrMiddle Then
        For counter = 1 To ptrMiddle - CountLeft + 1
            DataStore(counterMain + counter - 1) = TempStore(CountLeft + counter - 1)
        Next
    Else
        For counter = 1 To ending - CountRight + 1
            DataStore(counterMain + counter - 1) = TempStore(CountRight + counter - 1)
        Next
    End If
End Sub

Private Sub CreatePlayerHead()
    body = 0
    snake(0) = New PictureBox
    With snake(0)
        .Width = 15
        .Height = 15
        .BackColor = Color.Green
        .Top = Me.Height / 2 - snake(0).Height
        .Left = Me.Width / 2 - snake(0).Width
    End With

    Me.Controls.Add(snake(0))
End Sub
Private Sub PlayerSnakeBodyWithColour()
    Dim body_colour As Integer
    body += 1
    snake(body) = New PictureBox

    With snake(body)
        .Width = 15
        .Height = 15
        .Top = Me.Height + 100
        .Left = Me.Width + 100
    End With

    body_colour = Int(Rnd() * 8 + 1)
    Select Case body_colour
        Case 1
            snake(body).BackColor = Color.Green
            snake(body).TabIndex = 1
        Case 2
            snake(body).BackColor = Color.Blue
            snake(body).TabIndex = 2
        Case 3
            snake(body).BackColor = Color.Purple
            snake(body).TabIndex = 3
        Case 4
            snake(body).BackColor = Color.Red
            snake(body).TabIndex = 4
        Case 5
            snake(body).BackColor = Color.Yellow
            snake(body).TabIndex = 5
        Case 6
            snake(body).BackColor = Color.White
            snake(body).TabIndex = 6
        Case 7
            snake(body).BackColor = Color.Pink
            snake(body).TabIndex = 7
        Case 8
            snake(body).BackColor = Color.Orange
            snake(body).TabIndex = 8
    End Select
    Me.Controls.Add(snake(body))

    ReDim DataStore(body)

    For counter = 0 To body
        DataStore(counter) = snake(counter).TabIndex
    Next
    MergeSort(1, snake(body).TabIndex)
    For counter = 0 To body
       Textbox1.text = DataStore(counter) & vbCrLf
    Next
End Sub
End Class

I'm using a textbox as the output for the mean time to ensure the merge sort is working.
If anyone could help, it would mean a lot.Thank you.

[.paul.]

It looks like DataStore hasn't been assigned dimension

[.paul.]

If it isn't the DataStore array, it is definitely because you're trying to use an array index that is < 0 or > your array upperbound

[Furqan Raheem]

The DataStore array is assigned towards the end of the code to the length of body of the snake

[Inferrd]

I really do not understand what you are trying to do here.

You have an array of PictureBoxes, Snake(). Each PictureBox has a TabIndex whose value can be from 1 up to 8.

You store those TabIndex values in a parallel array, DataStore()

You merge sort that parallel array (DataStore()).

So you'll end up with the DataStore() array containing numbers 1 through 8 sorted in ascending order (apart from the first element, at index 0).

However, the contents of the DataStore() array bear no relationship to the Snake() array??


As to the IndexOutOfRange exception, I think you are trying to sort the DataStore() array from index 1 to the end of the array, so

MergeSort(1, snake(body).TabIndex)

should be

MergeSort(1, body)

and similarly

ReDim TempStore(snake(body).TabIndex)

should be

ReDim TempStore(body)

[passel]

Yeah, I don't see where you're tying the array of colors to the pictureboxes that have that color, so how does sorting the colors end up drawing the pictureboxes in sorted order.

It doesn't seem like you really need a sort, per se.
If you're going to have eight different colors for the body parts, just have an array of eight that you increment each element, one element for each color.

So, when you add a new body part, pick a random color, increment the corresponding index in your color array, then loop through that and use it to change the backcolor of your pictureboxes, in the order thay are in the original array.

Dim ColorCounters(7) As Integer
Dim ColorVals() as Color = {Color.Green, Color.Yellow, etc...}

part = 1
For colorIdx = 0 to 7
  For colorNum = 1 to ColorCounters(colorIdx)
     snake(part).BackColor = ColorVals(colorIdx)
     part += 1
  Next
Next

No need to use tabindex, or swap colors and pictureboxes around, or maintain a way of keeping track of what order the pictureboxes are in.

[Furqan Raheem]

I really do not understand what you are trying to do here.

You have an array of PictureBoxes, Snake(). Each PictureBox has a TabIndex whose value can be from 1 up to 8.

You store those TabIndex values in a parallel array, DataStore()

You merge sort that parallel array (DataStore()).

So you'll end up with the DataStore() array containing numbers 1 through 8 sorted in ascending order (apart from the first element, at index 0).

However, the contents of the DataStore() array bear no relationship to the Snake() array??


As to the IndexOutOfRange exception, I think you are trying to sort the DataStore() array from index 1 to the end of the array, so

MergeSort(1, snake(body).TabIndex)

should be

MergeSort(1, body)

and similarly

ReDim TempStore(snake(body).TabIndex)

should be

ReDim TempStore(body)

This sorted the problem thanks.

[Furqan Raheem]

Yeah, I don't see where you're tying the array of colors to the pictureboxes that have that color, so how does sorting the colors end up drawing the pictureboxes in sorted order.

It doesn't seem like you really need a sort, per se.
If you're going to have eight different colors for the body parts, just have an array of eight that you increment each element, one element for each color.

So, when you add a new body part, pick a random color, increment the corresponding index in your color array, then loop through that and use it to change the backcolor of your pictureboxes, in the order thay are in the original array.

Dim ColorCounters(7) As Integer
Dim ColorVals() as Color = {Color.Green, Color.Yellow, etc...}

part = 1
For colorIdx = 0 to 7
  For colorNum = 1 to ColorCounters(colorIdx)
     snake(part).BackColor = ColorVals(colorIdx)
     part += 1
  Next
Next

No need to use tabindex, or swap colors and pictureboxes around, or maintain a way of keeping track of what order the pictureboxes are in.

I know I don't need to use such a complicated algorithm. I'm doing my coursework and to get into the top mark band, I've included the merge sort.
I have not yet code for how the ordered list will become the snakes body.The sorting part is just the first part of a feature I'll include in the game.
If possible I will implement your code to the sorted list.
Thank you.

[Inferrd]

Having had the chance to think on this for a while, I suppose the DataStore() and Snake() arrays don't need a direct relationship.

Assuming you are not reordering the actual picture boxes in the Snake() array then, once you have performed the merge sort, you could simply iterate through both arrays updating the colour of the picture boxes based on the colour values stored in the DataStore() array.

Based on passel's code:

Dim ColorVals() as Color = {Color.Green, Color.Yellow, etc...}

For part = 1 To body
    snake(part).BackColor = ColorVals(DataStore(part) - 1)
Next

If you want to get rid of the -1, then you might want to use zero based values for the colour codes:

 body_colour = Int(Rnd() * 8)
 Select Case body_colour
     Case 0
        etc....

Also, one of the things that I found confusing when initially reading through your code was your use of the TabIndex to store the colour codes along with the PictureBoxes. It would be more usual to use the Tag Property (if you are not already using it for something else). The Tag Property stores Object Types, and so can be used for storing just about anything. When you retrieve the value from the Tag Property, you should convert it to the appropriate Type: CInt(snake(counter).Tag) in this case.

[passel]

I thought using TabIndex was a bit odd as well, but since the picturebox doesn't support input focus and doesn't use the TabIndex as a TabIndex, it isn't clobbered by the control as it would be by a control that does support input focus. I wouldn't have used it, but I guess it technically works without any apparent repercussions.

[Furqan Raheem]

Thank you very much.This cleared up a lot of stuffs. I will look into the tag property as tabindex isn't what I thought it was supposed to be. Really appreciate the further help on using the sorted list for the snakes body. Thank you.