I am attempting to implement an array using the shell sort algorithm. The program will sort the array and output each element to the Listbox after the button was clicked. However, the first item output is always 0. I have included a piece of my source code and a photo of the form below;
Dim randGen As New Random()
Dim unstArray() As Integer
Dim unstArrayCopy() As Integer
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 'Generates random number to save in array.
Dim i As Integer = CInt(TextBox1.Text)
ReDim unstArray(i)
ReDim unstArrayCopy(i)
For x = 0 To i
unstArray(x) = randGen.Next(1, 10001)
Next
Array.Copy(unstArray, unstArrayCopy, i)
End Sub
Private Sub ShllSrtBtn_Click(sender As Object, e As EventArgs) Handles shllSrtBtn.Click
shellsort(unstArrayCopy, unstArrayCopy.GetUpperBound(0))
End Sub
Sub shellsort(ByRef shellSort() As Integer, ByVal max As Integer)
Dim stopp%, swap%, limit%, temp%, k%
Dim x As Integer = CInt((max / 2) - 1)
Do While x > 0
stopp = 0
limit = max - x
Do While stopp = 0
swap = 0
For k = 0 To limit
If shellSort(k) > shellSort(k + x) Then
temp = shellSort(k)
shellSort(k) = shellSort(k + x)
shellSort(k + x) = temp
swap = k
End If
Next k
limit = swap - x
If swap = 0 Then stopp = 1
Loop
x = CInt(x / 2)
Loop
For i = 0 To shellSort.GetUpperBound(0)
ListBox1.Items.Add(shellSort(i))
Next i
End Sub
The problem is here:
ReDim unstArray(i)
ReDim unstArrayCopy(i)
In VB, when you initialize an array, you must give it the maximum index you want to use, not the intended array length as in other languages like C#.
Because of that, your code creates an array of length i+1, but you only loop from 0 to i when filling the array. So the last element at index i will always be zero.
You should set the initializer in these lines to i-1.
VB Array Reference
Related
Basically, I'm trying to loop through every pixel of a picture and check it against every pixel of another image. The problem is that it seems to just do this very slowly (I can no longer interact with the opened window, and Debug.WriteLine works). I want to be sure this is the problem rather than there just being something wrong with my code.
monPic and crop are dimmed as bitmaps at the top of my code.
Private Sub BtnCheck_Click(sender As Object, e As EventArgs) Handles btnCheck.Click
monPic = New Bitmap("../../../../" & picNum & ".png")
crop = New Bitmap("../../../../mm.png")
For x As Integer = 0 To monPic.Width - 1
Debug.WriteLine("level 1")
For y As Integer = 0 To monPic.Height - 1
Debug.WriteLine("level 2")
If CInt(monPic.GetPixel(x, y).A) <> 0 Then
For x2 As Integer = 0 To crop.Width - 1
Debug.WriteLine("level 3")
For y2 As Integer = 0 To crop.Height - 1
Debug.WriteLine("level 4")
If monPic.GetPixel(x, y).R = crop.GetPixel(x2, y2).R And monPic.GetPixel(x, y).G = crop.GetPixel(x2, y2).G And monPic.GetPixel(x, y).B = crop.GetPixel(x2, y2).B Then matches += 1
Next y2
Next x2
End If
Next y
Next x
lblMatches.Text = CStr(matches)
End Sub
This works quickly. It requires
Imports System.Security.Cryptography
Convert the 2 bitmaps to Byte arrays then hash with Sha256. Compare the hash.
Adapted from https://www.codeproject.com/Articles/9299/Comparing-Images-using-GDI
Private Function Compare(bmp1 As Bitmap, bmp2 As Bitmap) As String
Dim result = "It's a match!"
If Not (bmp1.Size = bmp2.Size) Then
result = "It's not even the same size"
Else
Dim ic As New ImageConverter
Dim btImage1(0) As Byte
btImage1 = CType(ic.ConvertTo(bmp1, btImage1.GetType), Byte())
Dim btImage2(0) As Byte
btImage2 = CType(ic.ConvertTo(bmp2, btImage2.GetType), Byte())
Dim shaM As New SHA256Managed
Dim hash1 = shaM.ComputeHash(btImage1)
Dim hash2 = shaM.ComputeHash(btImage2)
Dim i As Integer = 0
Do While i < hash1.Length AndAlso i < hash2.Length AndAlso result = "It's a match!"
If hash1(i) <> hash2(i) Then
result = "The pixels don't match"
End If
i = (i + 1)
Loop
End If
Return result
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim png1 As New Bitmap(path1)
Dim png2 As New Bitmap(path2)
Dim message = Compare(png1, png2)
MessageBox.Show(message)
End Sub
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 7 years ago.
I have a program that creates a list of 25 random numbers from 0 to 1,000. I have to buttons the first button will load a list box with the random numbers and the second button will sort the list of numbers from the smallest to largest which is where I implemented bubble sort code. Now the other list box that is supposed to hold the sorted numbers doesn't work properly it only shows one number instead of all of them.
Here is my code:
Option Strict On
Public Class Form1
Dim rn As Random = New Random
Dim Clicked As Long = 0
Dim numbers, sort As Long
Private Sub GenerateBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles GenerateBtn.Click
Clicked += 1
For x = 0 To 25
numbers = rn.Next(0, 1000)
RandomBox.Items.Add(numbers)
If Clicked >= 2 Then
RandomBox.Items.Clear()
Clicked = 1
End If
Next
End Sub
Private Sub SortBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SortBtn.Click
Dim Sorted() As Long = {numbers}
Dim Swapped As Boolean
Dim endOfArray As Integer = Sorted.Length - 1
Dim Tmp As Byte
While (Swapped)
Swapped = False
For I = 0 To endOfArray - 1
If Sorted(I) > Sorted(I + 1) Then
Tmp = CByte(Sorted(I))
Sorted(I) = Sorted(I + 1)
Sorted(I + 1) = Tmp
Swapped = True
End If
endOfArray = endOfArray - 1
Next
End While
SortBox.Items.Clear()
For I = 0 To Sorted.Count - 1
SortBox.Items.Add(Sorted(I))
Next
End Sub
End Class
Change your:
Dim Sorted() As Long = {numbers}
to
Sorted(x) = numbers
edit: Since you changed your code. You need to put back in the line that loads the Sorted Array.
For x = 0 To 25
numbers = rn.Next(0, 1000)
RandomBox.Items.Add(numbers)
Sorted(x) = numbers
If Clicked >= 2 Then
RandomBox.Items.Clear()
Clicked = 1
End If
Next
and remove the:
Dim Sorted() As Long = {numbers}
from the second part and put this declaration back in the beginning like you had:
Dim Sorted(26) as Long
The way you have will only show the latest random number. It is not any array but a single entity. Therefore only the latest will be add into the array. You need to load each number into the array as you create each one. Thus the (x) which loads it into position x.
You didn't use any arrays at all in your project...you're using the ListBox as your storage medium and that's a really bad practice.
I recommend you set it up like this instead:
Public Class Form1
Private rn As New Random
Private numbers(24) As Integer ' 0 to 24 = 25 length
Private Sub GenerateBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles GenerateBtn.Click
For x As Integer = 0 To numbers.Length - 1
numbers(x) = rn.Next(0, 1000)
Next
' reset the listbox datasource to view the random numbers
RandomBox.DataSource = Nothing
RandomBox.DataSource = numbers
' empty out the sorted listbox
SortBox.DataSource = Nothing
End Sub
Private Sub SortBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SortBtn.Click
' make a COPY of the original array that we will sort:
Dim sorted(numbers.Length - 1) As Integer
Array.Copy(numbers, sorted, numbers.Length)
Dim Swapped As Boolean = True
Dim endOfArray As Integer = Sorted.Length - 1
Dim Tmp As Integer
While (Swapped)
Swapped = False
For I As Integer = 0 To endOfArray - 1
If sorted(I) > sorted(I + 1) Then
Tmp = sorted(I)
sorted(I) = sorted(I + 1)
sorted(I + 1) = Tmp
Swapped = True
End If
Next
endOfArray = endOfArray - 1
End While
' reset the listbox datasource to view the sorted numbers
SortBox.DataSource = Nothing
SortBox.DataSource = sorted
End Sub
End Class
Also, note that you were decrementing endOfArray inside your for loop. You should only decrement it after each pass; so outside the for loop, but inside the while loop.
Additionally, you were using a Tmp variable of type Byte, but generating numbers between 0 and 999 (inclusive). The Byte type can only hold values between 0 and 255 (inclusive).
Your Bubble Sort implementation was very close to correct!
I started a new project which loads and saves tilesets in style of ini-datas.
The problem is now, that it loads the tiles into a 1d- list, which got copied sorted into a 1d-array.
Now I am trying to convert this sorted 1d-array into a 2d-array.
My try:
LoadedTiles.Sort(Function(p1, p2) (p1.Position.X.CompareTo(p2.Position.X)))
LoadedTiles.Sort(Function(p1, p2) (p1.Position.Y.CompareTo(p2.Position.Y)))
Dim currentArray(AmountTiles) As Tile
currentArray = LoadedTiles.ToArray
Dim lengthX, lengthY As Integer
Dim yAxis As Integer = currentArray(0).Position.Y
For Each p In currentArray
If Not p.Position.Y = yAxis Then
lengthX = (p.Position.X / p.Size.Width)
lengthY = (currentArray(currentArray.Length - 1).Position.Y / p.Size.Width)
Else
lengthX = (currentArray(currentArray.Length - 1).Position.X / p.Size.Width)
lengthY = 0
End If
Next
MapTiles = New Tile(lengthX, lengthY) {}
Dim ii As Integer
For x = 0 To lengthX
For y = 0 To lengthY
MapTiles(x, y) = currentArray(ii)
If Not ii >= currentArray.Length - 1 Then
ii += 1
End If
Next
Next
This gives a wrong output.
See picture below:
http://www.directupload.net/file/d/3690/pz8x98jr_png.htm
Is it possible to do it right?
Thanks alot!
The k-th element in a 1D array can correspond to row i=k/N and column j=k%N where N is the number of columns. The reverse is k=i*N+j
Ok guys, I got it ( =
Public Class Form1
Dim List As New List(Of Point)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
List.Add(New Point(180, 360))
List.Add(New Point(180, 180))
List.Add(New Point(180, 540))
'Convert 1d to 2d
Dim count As Point = countXYAxis(List, 180)
MsgBox(count.ToString)
Dim p(count.X - 1, List.Count - 1) As Point
MsgBox(p.Length)
Dim rofl As Integer
For i = 0 To p.GetUpperBound(0)
For j = 0 To p.GetUpperBound(1)
p(i, j) = List(rofl)
If Not rofl >= List.Count - 1 Then
rofl += 1
End If
Next
Next
For Each t In p
MsgBox(t.ToString)
Next
End Sub
Private Function countXYAxis(ByVal pt As List(Of Point), ByVal size As Integer) As Point
Dim bufferY As New List(Of Integer)
Dim cP As New Point
For Each pts In pt
If Not bufferY.Contains(pts.Y) Then
bufferY.Add(pts.Y)
End If
Next
For i = 0 To pt.Count - 1
If pt(i).Y = bufferY(0) Then
Else
cP = New Point(pt(i).X / size, bufferY.Count)
End If
Next
Return cP
End Function
End Class
I'm trying to loop this array 100 times (gets a number from 0-99,999). I've tried it several different ways with no luck. I've got it set up so you click a button and it generates the array. The user will then enter a number and hit the other button to check how many times that number shows up in the group of a 100 numbers. Any thoughts how to fix it? I'm stuck.
Dim i As Integer
Dim rnd As New Random()
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEnter.Click
Dim num As Integer
If Int32.TryParse(txtEnter.Text, num) AndAlso num >= 0 AndAlso num < 10 Then
lblNumber.Text = i.ToString()
Dim counts = From c In i.ToString()
Group By c Into Group
Select DigitGroup = New With {.Count = Group.Count(), .Digit = c, .Group = Group}
Order By DigitGroup.Count Descending, DigitGroup.Digit
Dim numCount = counts.FirstOrDefault(Function(grp) grp.Digit.ToString() = num.ToString())
If numCount IsNot Nothing Then
Dim numMessage = String.Format("There are {0} number {1}'s found.", numCount.Count, num)
MessageBox.Show(numMessage)
Else
MessageBox.Show("Your number does not contain a " & num)
End If
Else
MessageBox.Show("Please enter a number between 0 and 9.")
End If
End Sub
Private Sub btnGetNumber_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetNumber.Click
btnEnter.Enabled = True
i = 0
Do Until i > 100
Dim randomInt = rnd.Next(0, 100000)
i = i + 1
i = rnd.Next(0, 100000)
Loop
End Sub
End Class
First of all, it is common to use For Loops when you know the number of loops.
Secondly, you forgot to increment i in the until loop
Finally, you don't need to redeclare rnd in every loop. Something like that sounds better to me :
Dim rnd As New Random()
For i = 1 To 100
Dim randomInt = rnd.Next( 0 , 100000 )
Next
Move the New Random() out of that loop. Make it global and create the instance just one time.
(The Random generator starts using a seed obtained from the current time. Declaring a Random variable inside a loop result in the same seed used again and again. This gives back the same number defeating the randomness of the function) It is like: http://xkcd.com/221/
See another explanation here
Of course, if you don't increment the variable i used to control the loop, you will loop forever
Dim i As Integer
Dim rnd As New Random()
.....
i = 0
Do Until i > 100
Dim randomInt = rnd.Next(0, 100000)
i = i + 1
Loop
Said that, now I can't get what are you trying to do here. There is no array to check and you do not use the value obtained from the Random generator, simply, your i variable exits with value 101.
Now I am just guessing what are your intentions, but perhaps you want just this?
i = rnd.Next(0, 100000)
This will give to the variable i a random number and your subsequent code checks how many, of the required digit, are present in i
I see that you are not adding the variable "i" to increment:
i = 1
Do Until i > 100
Dim rnd As New Random()
Dim randomInt = rnd.Next(0, 100000)
i+=1 'Increment value of i by 1, same as i = i + 1
Loop
The variable of "i" will always be 1 if not incremented. Check that and let me know if that solves the problem!
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
lstBox.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?