Find Prime Numbers & Store Them In An Array (List)
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Find Prime Numbers & Store Them In An Array (List)
Here's a cool little snippet I wrote based on an idea that I seen from a C++ code floating around on another forum. This bit of code will find all prime numbers within a specified range of numbers, and write them to a text file.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
&&&&Dim t As New Thread(AddressOf StartThreadedSearch)
&&&&t.IsBackground = True
&&&&t.Start()
Private Sub StartThreadedSearch()
&&&&If InvokeRequired Then
&&&&&&&&Invoke(New MethodInvoker(AddressOf StartThreadedSearch))
&&&&&&&&Exit Sub
&&&&End If
&&&&Using sw As New StreamWriter(MyFilePathHere, True)
&&&&&&&&For Each Num As Long In FindPrimesInRange(0, 10000)
&&&&&&&&&&&&sw.WriteLine(Num.ToString)
&&&&&&&&Next
&&&&End Using
&&&&MessageBox.Show("Done")
Private Function FindPrimesInRange(RangeStart As Long, RangeEnd As Long) As List(Of UInt32)
&&&&If RangeEnd & RangeStart Then Throw New Exception("RangeEnd is less than RangeStart param")
&&&&Dim PrimeArray As New List(Of UInt32)
&&&&'2 is a prime number
&&&&If RangeStart &= 2 AndAlso RangeEnd &= 2 Then
&&&&&&&&PrimeArray.Add(2)
&&&&&&&&RangeStart = 2
&&&&End If
&&&&If RangeStart Mod 2 = 0 Then RangeStart += 1
&&&&For i As UInt32 = CUInt(RangeStart) To CUInt(RangeEnd) Step 2
&&&&&&&&If i = 3 OrElse i = 5 Then
&&&&&&&&&&&&PrimeArray.Add(i)
&&&&&&&&Else
&&&&&&&&&&&&Dim PrimeNum As Boolean = True
&&&&&&&&&&&&For x As UInt32 = 3 To CUInt((i \ 2))
&&&&&&&&&&&&&&&&If x && i Then
&&&&&&&&&&&&&&&&&&&&If i Mod x = 0 Then PrimeNum = False
&&&&&&&&&&&&&&&&End If
&&&&&&&&&&&&&&&&If x = (i \ 2) AndAlso PrimeNum = True Then
&&&&&&&&&&&&&&&&&&&&PrimeArray.Add(i)
&&&&&&&&&&&&&&&&End If
&&&&&&&&&&&&Next
&&&&&&&&End If
&&&&Return PrimeArray
End Function
This speeds up the process by minimizing the searching that it does by more than half... *Could optimize it more, but this is pretty much pointless anyways.
This post was last modified: 02-06- AM by .
Microsoft MVP .NET Programming - (2012 - Present)
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RE: Find Prime Numbers & Store Them In An Array (List)
Here's the output from 0 - 10000:
Microsoft MVP .NET Programming - (2012 - Present)
(R)Crestron DMC-T Certified Automation Programmer
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Posts: 9,688
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Joined: Jun 2011
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RE: Find Prime Numbers & Store Them In An Array (List)
Feel free to add to this if you can, I was just looking for some cool projects to try out and present for a new system soon to be at TLF for learning VB :)
Microsoft MVP .NET Programming - (2012 - Present)
(R)Crestron DMC-T Certified Automation Programmer
Development Site:
Posts: 9,688
Threads:1,013
Joined: Jun 2011
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RE: Find Prime Numbers & Store Them In An Array (List)
I just went through 0 - 100 000 range But I think it could be split up so that the array doesn't hold all the values at once, for example output an array holding the values every difference of 10000 in the total range to the file at a time. That could speed it up...
Microsoft MVP .NET Programming - (2012 - Present)
(R)Crestron DMC-T Certified Automation Programmer
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