Populating 2 dimensional array using a For loop - vb.net

Currently I'm trying to fill a 3x3 square with random x's and o's to make a tic tac toe
game. Unfortunately the game doesn't seem to output all the x's and o's. Logically, from what I can see, it should be able to but it's not. Any help would be appreciated.
Shared Sub twodimension()
Dim tic(2, 2) As String
Dim min As Integer
Dim x As String
Dim random As New Random()
Dim i As Integer
Dim x1 As Integer
Dim bound0 As Integer = tic.GetUpperBound(0)
Dim bound1 As Integer = tic.GetLowerBound(1)
For i = 0 To bound0
For x1 = 0 To bound1
min = random.Next(2)
If min = 0 Then
x = "x"
Console.WriteLine("{0}", x)
Else
x = "o"
Console.WriteLine("{0}", x)
End If
Console.Write(" "c)
Next
Console.WriteLine()
Next
End Sub

So presumably you've got this declaration somewhere, right?
Public Shared Tic(2, 2) As String
In your code you've got GetLowerBound which will (almost) always returns zero and instead you should have GetUpperBound().
Dim bound0 As Integer = tic.GetUpperBound(0)
Dim bound1 As Integer = Tic.GetUpperBound(1)
EDIT (in response to comment)
GetUpperBound(int) returns the highest number that you can use for the dimension that you specify.
So for the following array:
Dim MyArray(4, 6, 8) As Integer
Trace.WriteLine(MyArray.GetUpperBound(0)) ''//Returns 4
Trace.WriteLine(MyArray.GetUpperBound(1)) ''//Returns 6
Trace.WriteLine(MyArray.GetUpperBound(2)) ''//Returns 8
GetLowerBound(int) returns the lowest number that you can use for the dimension that you specify. In almost every case this is zero but in older versions of VB (and using some COM interop) you can create arrays that don't "start" at zero and instead start at whatever you wanted. So in old VB you could actually say Dim Bob(1 To 4) As Integer and GetLowerBound(0) would return 1 instead of 0. For the most part there is no reason to even be aware that GetLowerBound exists even.

Related

Convert 32-bit signed integer to 64-bit integer while preserving the exact bits

I have a 32-bit value that is stored in the VB.Net type Integer (i.e. Int32.) I am only interested in the bits - not the numerical value. Sometimes the 32nd bit is a one which is interpreted as a negative number. My goal is to reverse the actual bits. My original data is encoded into bits right-to-left (LSB right-most) and is read back in left-to-right (MSB left-most.) I am adapting someone else's code and design. One thought I had was maybe to convert to a long temporarily but I don't know how to do that and preserve the 32nd bit correctly.
Public Shared Function ReverseBits32(ByVal n As Integer) As Integer
Dim result As Integer = 0
For i As Integer = 0 To 32 - 1
result = result * 2 + n Mod 2
n = n >> 1 'n Or 2
Next
Return result
End Function
If you had a method to reverse the bits of a byte you could apply it four times to the bytes of an integer. A little research finds Bit Twiddling Hacks.
Module Module1
Sub ShowBits(a As Integer)
Dim aa = BitConverter.GetBytes(a)
Console.WriteLine(String.Join(" ", aa.Select(Function(b) Convert.ToString(b, 2).PadLeft(8, "0"c))))
End Sub
Function ReverseBits(b As Byte) As Byte
' From https://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith32Bits
Dim c = CULng(b)
Return CByte((((c * &H802UL And &H22110UL) Or (c * &H8020UL And &H88440UL)) * &H10101UL >> 16) And &HFFUL)
End Function
Function ReverseBits(a As Integer) As Integer
Dim bb = BitConverter.GetBytes(a)
Dim cc(3) As Byte
For i = 0 To 3
cc(3 - i) = ReverseBits(bb(i))
Next
Return BitConverter.ToInt32(cc, 0)
End Function
Sub Main()
Dim y = -762334566
ShowBits(y)
y = ReverseBits(y)
ShowBits(y)
Console.ReadLine()
End Sub
End Module
Output from test value:
10011010 10110010 10001111 11010010
01001011 11110001 01001101 01011001
I used the "no 64-bit" method because it is written for a language where arithmetic overflow is ignored - the methods using 64-bit operations rely on that but it is not the default for VB.NET.

Using visual basic, what do I need to add to my for next loop to make my application display only even numbers?

My question is not the same as the one it is flagged as similar to. I need my application to display the actual numbers that are even in a range of numbers entered by the user. The other question prints "Even" or "Odd" based on a number.
I am working on a homework assignment where I have to make my application take numbers that are input by the user in text boxes and display the even numbers between them in a list box using a For...Next statement.
(So if the user enters 2 in the From box and 10 in the To box it, the application needs to output 2, 4, 6, 8, and 10 without commas in the list box.)
This is my current interface (Showing how the application runs with the current code):
Numbers App Test
This is my current code:
Dim intFrom As Integer
Dim intTo As Integer
Integer.TryParse(txtFrom.Text, intFrom)
Integer.TryParse(txtTo.Text, intTo)
lstNumbers.Items.Clear()
For intList As Integer = intFrom To intTo
If intFrom >= intTo Then
Exit For
End If
lstNumbers.Items.Add(intList)
Next intList
End Sub
Replace your For cycle with this:
For intList As Integer = intFrom To intTo
Dim result As Integer = intList Mod 2
If result = 0 Then
lstNumbers.Items.Add(intList)
End If
Next
Alternatives
lstNumbers.Items.Clear()
'alternative 1
Dim ie As IEnumerable(Of String)
ie = From i In Enumerable.Range(intFrom, intTo - intFrom + 1)
Where (i And 1) = 0 Select CType(i, String)
lstNumbers.Items.AddRange(ie.ToArray)
lstNumbers.Items.Clear()
'alternative 2
For intList As Integer = intFrom To intTo
If (intList And 1) = 0 Then
lstNumbers.Items.Add(intList)
End If
Next

Add integer to another integer in vb.net?

How can I add an integer to another integer in vb.net?
This is what I need to do:
Given integer: 2187 ->
Converted integer: 2018
I need to add a 0 in between the first and second number, and drop the last digit. This will give me the year.
Here is the code that I have:
Protected Function GetYear(ByVal term As Integer) As Integer
Dim termYear As String = Convert.ToString(term)
termYear.Substring(0, 2)
termYear.Insert(1, "0")
Dim convertedYear As Integer
Int32.TryParse(termYear.ToString, convertedYear)
convertedYear = convertedYear / 10
Return convertedYear
End Function
In general strings are immutable. So you'd have to create a new string out of the addition of substrings. Check this possible solution.
Function GetYear(ByVal term As Integer) As Integer
Dim termYear As String = Convert.ToString(term, Globalization.CultureInfo.InvariantCulture)
Dim result As String = termYear.Substring(0, 1) + "0" + termYear.Substring(1, 2)
Return Int32.Parse(result)
End Function
Strings are immutable, when you do any changes with one of their method, you need to get the returned string.
termYear = termYear.Insert(1, "0")
This question deserves a math based solution. The below code specifies the zero insertion point relative to the number's right side instead of the left as stated in the problem statement. So for a 4 digit number the insertion point is 3 versus 2. It also allows you to change the insertion point.
Private Function GetYear(ByVal term As Integer, Optional zeroDigitPosition As Integer = 3) As Integer
If zeroDigitPosition > 0 Then
Dim divisor As Integer = 1
For i As Integer = 1 To zeroDigitPosition - 1
divisor *= 10
Next
Dim ret As Integer = term \ 10 ' drop one's place digit, remaining digits shift to right
Dim rightShiftedDigits As Integer = ret Mod divisor
Dim remainder As Integer = Math.DivRem(ret, divisor, rightShiftedDigits)
' shift the remainder to the left by divisor * 10
' (remember first right shift invplved \ 10) and add
' rightShiftedDigits to yield result
Return (remainder * divisor * 10) + rightShiftedDigits
Else
Throw New ArgumentOutOfRangeException("zeroDigitPosition must be greater then zero")
End If
End Function

Random numbers in array without any duplicates

I'm trying to randomize an array from numbers 0 to 51 using loops but I just cannot seem to pull it off. My idea was that
Generate a Random Number
Check if this random number has been used by storing the previous in an array
If this random number has been used, generate new random number until it is not a duplicate
If it's not a duplicate, store it
My attempt:
Dim list(51) As Integer
Dim templist(51) As Integer
For i As Integer = 0 To 51 Step 1
list(i) = i
Next i
Do While counter <= 51
p = rand.Next(0, 52)
templist(counter) = p
For n As Integer = 0 To 51 Step 1
p = rand.Next(0, 52)
If templist(n) = p Then
Do While templist(n) = p
p = rand.Next(0, 52)
Loop
templist(n) = p
Else
templist(n) = p
End If
Next
counter += 1
Loop
For n As Integer = 0 To 51 Step 1
ListBox1.Items.Add(templist(n))
Next
It will be a lot easier if you just have a list of all of the possible numbers (0 to 51 in your case), then remove the number from the list so it can't be picked again. Try something like this:
Dim allNumbers As New List (Of Integer)
Dim randomNumbers As New List (Of Integer)
Dim rand as New Random
' Fill the list of all numbers
For i As Integer = 0 To 51 Step 1
allNumbers.Add(i)
Next i
' Grab a random entry from the list of all numbers
For i As Integer = 0 To 51 Step 1
Dim selectedIndex as Integer = rand.Next(0, (allNumbers.Count - 1) )
Dim selectedNumber as Integer = allNumbers(selectedIndex)
randomNumbers.Add(selectedNumber)
allNumbers.Remove(selectedNumber)
' Might as well just add the number to ListBox1 here, too
ListBox1.Items.Add(selectedNumber)
Next i
If your goal is to get the numbers into ListBox1, then you don't even need the "randomNumbers" list.
EDIT:
If you must have an array, try something like this:
Function RandomArray(min As Integer, max As Integer) As Integer()
If min >= max Then
Throw New Exception("Min. must be less than Max.)")
End If
Dim count As Integer = (max - min)
Dim randomNumbers(count) As Integer
Dim rand As New Random()
' Since an array of integers sets every number to zero, and zero is possibly within our min/max range (0-51 here),
' we have to initialize every number in the array to something that is outside our min/max range.
If min <= 0 AndAlso max >= 0 Then
For i As Integer = 0 To count
randomNumbers(i) = (min - 1) ' Could also be max + 1
Next i
End If
Dim counter As Integer = 0
' Loop until the array has count # of elements (so counter will be equal to count + 1, since it is incremented AFTER we place a number in the array)
Do Until counter = count + 1
Dim someNumber As Integer = rand.Next(min, max + 1)
' Only add the number if it is not already in the array
If Not randomNumbers.Contains(someNumber) Then
randomNumbers(counter) = someNumber
counter += 1
End If
Loop
Return randomNumbers
End Function
This is good enough for your assignment, but the computer scientist in my hates this algorithm.
Here's why this algorithm is much less desirable. If zero is in your range of numbers, you will have to loop through the array at least 2N times (so 104+ times if you are going from 0 to 51). This is a best case scenario; the time complexity of this algorithm actually gets worse as the range of numbers scales higher. If you try running it from 0 to 100,000 for example, it will fill the first few thousand numbers very quickly, but as it goes on, it will take longer and longer to find a number that isn't already in the list. By the time you get to the last few numbers, you could potentially have randomly generated a few trillion different numbers before you find those last few numbers. If you assume an average complexity of 100000! (100,000 factorial), then the loop is going to execute almost ten to the half-a-millionth power times.
An array is more difficult to "shuffle" because it is a fixed size, so you can't really add and remove items like you can with a list or collection. What you CAN do, though, is fill the array with your numbers in order, then go through a random number of iterations where you randomly swap the positions of two numbers.
Do While counter <= 51
p = rand.Next(0, 52)
While Array.IndexOf(list, p) = -1
p = rand.Next(0, 52)
End While
counter += 1
Loop
Haven't written VB in about 5 years, but try this out:
Function GetRandomUniqueNumbersList(ByVal fromNumber As Integer, ByVal toNumber As Integer) As List(Of Integer)
If (toNumber <= fromNumber) Then
Throw New ArgumentException("toNumber must be greater than fromNumber", toNumber)
End If
Dim random As New Random
Dim randomNumbers As New HashSet(Of Integer)()
Do
randomNumbers.Add(random.Next(fromNumber, toNumber))
Loop While (randomNumbers.Count < toNumber - fromNumber)
Return randomNumbers.ToList()
End Function
Ok, that was painful. Please someone correct it if I made any mistakes. Should be very quick because it's using a HashSet.
First response to forum on stackoverflow - be gentle.
I was looking for a way to do this but couldn't find a suitable example online.
I've had a go myself and eventually got this to work:
Sub addUnique(ByRef tempList, ByVal n, ByRef s)
Dim rand = CInt(Rnd() * 15) + 1
For j = 0 To n
If tempList(j) = rand Then
s = True
End If
Next
If s = False Then
tempList(n) = rand
Else
s = False
addUnique(tempList, n, s)
End If
End Sub
Then call the sub using:
Dim values(15) As Byte
Dim valueSeen As Boolean = False
For i = 0 To 15
addUnique(values, i, valueSeen)
Next
This will randomly add the numbers 1 to 16 into an array. Each time a value is added, the previous values in the array are checked and if any of them are the same as the randomly generated value, s is set to true. If a value is not found (s=false), then the randomly generated value is added. The sub is recursively called again if s is still true at the end of the 'For' loop. Probably need 'Randomize()' in there somewhere.
Apologies if layout is a bit wobbly.

integer to string problems

I'm trying to make a slot machine program. This procedure that I'm trying to do will assign a name to 3 randomly generated numbers. For some reason I'm getting a conversion error saying that it cant convert the integer to a string. I tried cstr() as well but the problem persisted
Sub GenerateNumbers()
Dim numbers(2) As Integer
Dim names(5) As String
Dim x As Integer
names(0) = "Cherries"
names(1) = "Oranges"
names(2) = "Plums"
names(3) = "Bells"
names(4) = "Melons"
names(5) = "Bar"
For x = 0 To 2
numbers(x) = names(CInt(Int((6 * Rnd()) + 1)))
Next x
End Sub
gives me error: conversion from string "Oranges" to type 'Integer' is not valid
The problem is that you are getting a random string from the names array and trying to assign it to numbers, which is declared as an array of integers. Of course this is not gonna work.
Apart from that, there is also the issue with out of bounds index as Eric pointed out.
Edit in response to comments:
To get the text values of those randomly generated slot machine results you just need to declare the array to store results as strings, same way as names is declared.
To be able to get the results from a separate procedure, you need to change it from Sub to Function, which is a procedure that can return a value, an array of strings in this case. Then you can call this function from your Main or any other procedure and store the returned value in a variable.
I also corrected the part with random result generation.
Module SlotMachine
Sub Main()
Dim slotResults As String()
'Get the results
slotResults = GenerateResults()
'Some further processing of results here, e.g. print results to console
For Each item In slotResults
Console.WriteLine(item)
Next
'Wait for keypress before closing the console window
Console.ReadLine()
End Sub
'Generates random results
Function GenerateResults() As String()
Dim results(2) As String
Dim names(5) As String
Dim x As Integer
names(0) = "Cherries"
names(1) = "Oranges"
names(2) = "Plums"
names(3) = "Bells"
names(4) = "Melons"
names(5) = "Bar"
Randomize()
For x = 0 To 2
results(x) = names(Int(6 * Rnd()))
Next x
Return results
End Function
End Module
Int(6 * Rnd()) will get you 0-5, if you +1, then overflow