I'm on visual basic and I'm reading through some piece of code my teacher wrote, he had this chunck of code:
Private Sub btnDividing_Click(sender As Object, e As EventArgs) Handles btnDividing.Click
Dim number As Integer = InputBox("Divide number by 2:")
Dim result As Integer = 0
Do While (number <> 0)
result += 1
number = number - 2
Loop
MsgBox("The result is: " & result, MsgBoxStyle.Exclamation)
End Sub
So my teacher typed the result += 1 and number = number -2 I didn't really understand that part so i tried simplifying it by changing it to:
Dim number As Integer = InputBox("Divide number by 2:")
Dim result As Integer = 0
Do While (number <> 0)
result = number / 2
Loop
MsgBox("The result is: " & result, MsgBoxStyle.Exclamation)
End Sub
but it keeps freezing after I click "OK"
Any suggestions?
It freezes because you made it an infinite loop:
Do While (number <> 0)
result = number / 2
Loop
The loop checks the value of number, but your modified code in the loop never modifies the value of number. So if the condition is true the first time it's checked, it will always be true. The original code modified the value:
Do While (number <> 0)
result += 1
number = number - 2
Loop
Since number is decremented by 2 with each iteration of the loop, it will eventually (assuming it's even) be equal to 0, making the loop condition false and the loop will end.
Basically, a loop needs to in some way modify the values being checked in the condition (or have some other control statement to exit the loop) or the loop will infinitely run.
Related
I am writing code for a form that is supposed to determine whether a value inputted by the user is valid as a check digit. They input a 13 digit number and it should determine whether or not the last value is valid as a check digit. I have written in the code for the check digit algorithm but I'm having trouble with comparing the value that the algorithm found with what the user input. I have tried using the substring method to compare the 13th number given by the user with the check digit that the algorithm determined but I am having issues with the syntax of everything.
This is the code I have been working on:
Private Sub btnValidate_Click(sender As Object, e As EventArgs) Handles btnValidate.Click
Dim intDigit As Integer
Dim intTotalOdd As Integer
Dim intTotalEven As Integer
Dim intGrandTotal As Integer
Dim intRemainder As Integer
Dim intCheckDigit As Integer
If txtNumber.Text.Length = 13 Then
For intOdd As Integer = 1 To 11 Step 2
intTotalOdd += (intDigit * 3)
Next intOdd
For intEven As Integer = 0 To 10 Step 2
intTotalEven += intDigit
Next intEven
intGrandTotal = intTotalOdd + intTotalEven
intRemainder = intGrandTotal Mod 10
If intRemainder <> 0 Then
intCheckDigit = 10 - intRemainder
End If
If txtNumber.Text.Substring(12, 13) = intCheckDigit Then
lblStatus = "Valid"
Else
lblStatus = "Not Valid"
End If
End If
End Sub
I think the way I'm doing it should work but I don't have very much to reference on how I would go about making the syntax work. Will the way that I'm trying to do it work or do I need to go about it in a different way?
Consider the following code :
Private Sub DelButton_Click(sender As Object, e As EventArgs) Handles DelButton.Click
If OrderListBox.Text = "" = False Then
For i As Integer = OrderListBox.SelectedIndex To arr.Count - 1
arr.RemoveAt(i)
Next
OrderListBox.Items.Remove(OrderListBox.SelectedItem)
End If
calculate()
End Sub
The program crashes at arr.RemoveAt(i) and displays the following error:
Index was out of range. Must be non-negative and less than the size
of the collection.
First of all, please note that in VB.NET and C#, FOR loops are implemented differently!
In VB.NET, it works like this:
BEFORE the loop starts, you are determining start and end of the loop:
Start = OrderListBox.SelectedIndex
End = arr.Count-1
Then, the loop starts.
It is important to know, that in VB.NET, the end of the loop is NOT calculated again anymore. This is an important difference to C#. In C#, the end of the loop is calculated before each single loop.
And now, in the loop, you are DELETING records from the array.
Therefore, the count of records in the array is DECREASING.
However, your loop is going on, since you have calculated the count of records in the array before the loop started.
Therefore, you are going beyond the range of the array.
You could rewrite your code as follows:
Dim i as Integer
i = OrderListBox.SelectedIndex
while i < arr.Count
arr.RemoveAt(i)
Next
This article covers details about the for loop in VB.NET, especially the section "Technical Implementation": https://msdn.microsoft.com/en-us/library/5z06z1kb.aspx
This error will be thrown when you try to remove an item at an index greater than the size of the collection. i.e when i is greater than arr.Count - 1.
You should make sure that OrderListBox.SelectedIndex is not greater than arr.Count - 1. Because if it does, you remove an item that, well, does not exists.
This code is actually displayed in the MSDN docs. As stated, you should do something like this:
Private Sub RemoveTopItems()
' Determine if the currently selected item in the ListBox
' is the item displayed at the top in the ListBox.
If listBox1.TopIndex <> listBox1.SelectedIndex Then
' Make the currently selected item the top item in the ListBox.
listBox1.TopIndex = listBox1.SelectedIndex
End If
' Remove all items before the top item in the ListBox.
Dim x As Integer
For x = listBox1.SelectedIndex - 1 To 0 Step -1
listBox1.Items.RemoveAt(x)
Next x
' Clear all selections in the ListBox.
listBox1.ClearSelected()
End Sub 'RemoveTopItems
ListBox.SelectedIndex will return a value of negative one (-1) is returned if no item is selected.
You didn't check it in your code.
Change your code to this:
If OrderListBox.SelectedIndex >= 0 And OrderListBox.Text = "" = False Then
EDIT
Your code is this:
For i As Integer = OrderListBox.SelectedIndex To arr.Count - 1
arr.RemoveAt(i)
Next
Let's say your OrderListBox contains 3 items : [A, B, C] and the SelectedIndex is 0
Then your code will:
Remove (0) ===> [B, C]
Remove (1) ===> [B]
Remove (2) ===> Exception!
You need to reverse the loop
For i As Integer = arr.Count - 1 To OrderListBox.SelectedIndex Step -1
arr.RemoveAt(i)
Next
I am trying to create a bowling program that will display the scores given in a multi-line text box. I've manage to get the program giving an output, but when it runs it skips asking for new inputs and just gives 5 0s on seperate lines and nothing else. I'm completely lost, any help is very much appreciated
EDIT: Sorry should have changed errors to reflect the programs changes, it looks like this now. It gives 0's instead of using the value I gave it, but it does ask for each input now.
For gameNumber As Integer = 1 To 5 Step 1
lblEnterScore.Text = "Enter Score for game #" & gameNumber
Dim Testint As Integer ' define an Integer for testing
Try
Testint = CInt(txtScoreInput.Text) ' try to convert whatever they entered to Int
Catch
MessageBox.Show("Entry is not an Integer") ' If you are here then the CInt failed for some reason, send a message
txtScoreInput.SelectAll()
txtScoreInput.Focus()
Exit Sub
End Try
If txtScoreInput.Text.Contains(".") Then
MsgBox("Bowling Score must be a whole number.")
txtScoreInput.SelectAll()
txtScoreInput.Focus()
Exit Sub
End If
If txtScoreInput.Text > MAXIMUM_SCORE Or txtScoreInput.Text < MINIMUM_SCORE Then
MsgBox("Bowling Score must be between 1 and 300.")
txtScoreInput.SelectAll()
txtScoreInput.Focus()
Exit Sub
End If
scoreInput(gameNumber) = CInt(txtScoreInput.Text)
' and store it in the array
' and increment the gamecounter for the next time through the loop
Next
'btnEnterScore.Enabled = False
' place the good score into the multi-line textbox
txtScoreOutputs.Text = gameScore & vbCrLf & txtScoreOutputs.Text
End Sub
If it was me, here's what I would do... Just a suggestion; I also cut out over half of your code and stopped it from throwing exceptions as well... You can put this in a click event or where ever you need it as well. You can modify this as well to take as many as you want from user input as well not just limit them from entering score's. Your user also has the option to get out of that loop when they choose to do so as well, not keeping them inside the loop...
Private ScoreLists As New List(Of Integer) 'Hold your inputted values
Private Const MAXIMUM_SCORE As Integer = 300 'Max score
Private Const MINIMUM_SCORE As Integer = 1 'Min score
Private blnStop As Boolean = False
Try
For gameNumber As Integer = 1 To 5
Dim intScore As Integer = 0
Do Until (intScore >= MINIMUM_SCORE And intScore <= MAXIMUM_SCORE) OrElse blnStop
If Not Integer.TryParse(InputBox("Please enter a score for game # " & gameNumber.ToString), intScore) Then
If MsgBox("Bowling Score must be a whole number. Stop getting scores?.", MsgBoxStyle.YesNo) = MsgBoxResult.Yes Then
blnStop = True
Exit For
End If
End If
Loop
ScoreLists.Add(intScore)
Next
'Display the results...
For i As Integer = 0 To ScoreLists.Count - 1
txtScoreOutputs.Text &= ScoreLists.Item(i.ToString)
Next
ScoreLists.Clear()
Catch ex As Exception
End Try
Construct your logic like this (pseudo):
Loop
{
AskUserForInput()
ProcessUserInput()
}
The loop part will control how many scores the user is prompted to enter. The AskUserForInput() function will prompt the user to type in a new score, and the ProcessUserInput() function will get the value and store it in an array or print it to the screen, etc.
Your current logic is not waiting for any new user input before trying to add to the scores. You are also getting zeros because you're setting the txtScoreOutputs with gameScore, which doesn't look like it's been set to the user's input.
I want to know why this loop doesn't show anything in VB.NET.
I think this code will create an infinite loop. But it doesn't show anything.
Dim i as Integer
For i = 1 to 3 Step - 1
MessageBox.Show(i)
Next
Is that loop different with this code (in java/c#) ?
for(int i = 1;i <= 3;i--)
{
// print i
}
http://msdn.microsoft.com/en-us/library/5z06z1kb.aspx
With a negative step size the loop only executes if counter >= end. So in this case with i = 1, that is less than the ending value so the loop doesn't execute at all.
It doesn't show anything because you are running the counter backwards without reversing the start and end conditions.
Think of the loop like this:
Dim counter As Int32 = 1
Do
If counter <= 1 Then
Exit Do
End If
Console.WriteLine("The counter is at " & counter)
counter +=1
Loop
Obviously this won't work properly.
You need to reverse the start and end conditions:
For counter = 3 To 1 Step -1
Console.WriteLine("counter: " & counter)
Next
For i = 1 to 3 Step - 1
It won't create an infinite loop. The loop will simply be skipped, because you can't get from 1 to 3 with a step value of -1.
Is that loop different with this code (in java/c#) ?
This loop will also end immediately, because the initial value (i = 1) meets the exit condition (i <= 3).
This code generates a stack overflow. I'm aware it is caused by the procedure calling itself.
What can I do to avoid the stack overflow? Recalling the sub procedure and generating a new random number is the easiest thing to do, however it generates the overflow. The randomly generated number picks a random inventory item, then the if statement matches that number (random inventory item) with the quantity of that item from the deck inventory to make sure it isn't less than 1. If the inventory of that item is 0, the else plays and restarts the procedure, generating a new random number and doing the process all over again. In another procedure I have a function that if the deck's inventory becomes completely empty, then the discard pile replenishes the deck, making the discard pile empty, so there should never be a case where all randomly generated numbers can be associated item with a inventory of 0.
I wonder if I could somehow force the random number generator
Number = (DeckGroup(Rnd.Next(0, DeckGroup.Count)).ID)
not to generate numbers to inventory items DeckGroup(Number).QuantityInteger that are zero. By doing so I wouldn't even need to recall the function.
The random number is generated by a different branch in the same structure group.
Private Sub PlayElse()
Dim CardCheckBoxArray() As CheckBox = {CardCheckBox1, CardCheckBox2, CardCheckBox3, CardCheckBox4, CardCheckBox5}
'Reset Number Generator
Number = (DeckGroup(Rnd.Next(0, DeckGroup.Count)).ID)
Dim PlayerQuantitySubtractionInteger As Integer
For PlayerQuantitySubtractionInteger = ChecksDynamicA To ChecksDynamicB
If CardCheckBoxArray(TextBoxInteger).Checked = True And DeckGroup(Number).QuantityInteger > 0 Then
DeckGroup(Number).QuantityInteger -= 1
'Select the Player depending value of T
Select Case T
Case 0
Player1HandGroup(Number).QuantityInteger += 1
Case 1
Player1HandGroup(Number).QuantityInteger2 += 1
Case 2
Player1HandGroup(Number).QuantityInteger3 += 1
Case 3
Player1HandGroup(Number).QuantityInteger4 += 1
Case 4
Player1HandGroup(Number).QuantityInteger5 += 1
End Select
CardTypeArray(PlayerQuantitySubtractionInteger) = Player1HandGroup(Number).CardType
CardCheckBoxArray(TextBoxInteger).Text = Player1HandGroup(Number).CardNameString
NumberArray(PlayerQuantitySubtractionInteger) = Number
Else
If CardCheckBoxArray(TextBoxInteger).Checked = True And DeckGroup(Number).QuantityInteger < 0 Then
Call PlayElse()
End If
End If
Next PlayerQuantitySubtractionInteger
End Sub
You could use LINQ to weed out all the objects you never want to get first and then use the collection returned by the linq instead of your original collection.
Something like:
Private Sub PlayElse()
Dim CardCheckBoxArray() As CheckBox = {CardCheckBox1, CardCheckBox2, CardCheckBox3, CardCheckBox4, CardCheckBox5}
'Reset Number Generator
Dim temp As IEnumerable(Of LunchMoneyGame.LunchMoneyMainForm.Group) = From r In DeckGroup Where r.QuantityInteger > 0 Select r
If temp IsNot Nothing AndAlso temp.Any Then
Number = (temp(Rnd.Next(0, temp.Count)).ID)
' ** Edit **: This will ensure that you only got 1 object back from the LINQ which can tell you whether or not you have bad data. You *can* exclude this check but its good practice to include it.
Dim obj As LunchMoneyGame.LunchMoneyMainForm.Group = Nothing
Dim t = From r In temp Where r.ID = Number Select r
If t IsNot Nothing AndAlso t.Count = 1 Then
obj = t(0)
End If
If obj IsNot Nothing Then
Dim PlayerQuantitySubtractionInteger As Integer
For PlayerQuantitySubtractionInteger = ChecksDynamicA To ChecksDynamicB
' ** Edit **
obj.QuantityInteger -= 1
'Select the Player depending value of T
Select Case T
Case 0
Player1HandGroup(Number).QuantityInteger += 1
Case 1
Player1HandGroup(Number).QuantityInteger2 += 1
Case 2
Player1HandGroup(Number).QuantityInteger3 += 1
Case 3
Player1HandGroup(Number).QuantityInteger4 += 1
Case 4
Player1HandGroup(Number).QuantityInteger5 += 1
End Select
CardTypeArray(PlayerQuantitySubtractionInteger) = Player1HandGroup(Number).CardType
CardCheckBoxArray(TextBoxInteger).Text = Player1HandGroup(Number).CardNameString
NumberArray(PlayerQuantitySubtractionInteger) = Number
Next PlayerQuantitySubtractionInteger
End If
End If
End Sub
Pass through the list and determine only those that are valid. Then randomly pull from that set. Here is a simple version of it. You could use LINQ as well, but this should be clear enough:
Dim validDeckGroupsIndexes As New List(Of Integer)
For ndx As Integer = 0 to DeckGroup.Count - 1
If DeckGroup(ndx).QuantityInteger > 0 Then
validDeckGroupsIndexes .Add(ndx)
End If
Next ndx
Then use this:
Dim deckGroupNdx As Integer = Rnd.Next(0, validDeckGroupsIndexes.Count)
Number = DeckGroup(deckGroupNdx).ID