Listing Prime Factors in VB.Net

Finding Prime Factors in Visual Basic (VB.Net)

Finding prime factors is all about selecting those factors of a number that are prime.
The prime factors of 36 as an example, are:

2 X 2 X 3 X 3.

Prime Factor VB.Net code

We'll go about the code in a simple way:

Step 1:

Starting with 2, find the first factor of the number of interest - this factor will definitely be a prime.
Store this factor away.

Step 2:

Divide number in question by found factor.

Step 3:

Using result from Step 2 as the new number in question (number whose prime factors we are trying to find), repeat Step 1.

Step 4:

Continue recursively until we arrive at 1.

Step 5:

We'll use the square-root of number range.

Create a new class file; Project, Add Class.
Call it listPrimeFactors.vb.
Optionally, create a new module file; Project, Add Module.
Call it ListPrimeFactorsModule.vb.

Type out the adjoining Visual Basic (VB.Net) code for finding prime numbers.

Note: You can just reuse the main module from the previous lesson if you have been following.

VB.Net code for listPrimeFactors Class File.

Public Class ListPrimeFactors

    Dim find_my_factors As Integer
    Dim found_prime_factors As New List(Of Integer)
    Dim sqrt_range As Integer

    Public Sub _init_(value As Integer)
        find_my_factors = value
    End Sub

    ' takes one argument, the candidate For factorisation
    ' returns an array reference Of the prime factors
    Public Function onlyPrimeFactors() As List(Of Integer)
        Dim temp_limit = Math.Ceiling(Math.Sqrt(find_my_factors))

        ' STEP 1:
        Dim i = 2
        Do While i <= temp_limit
            ' STEP 4:
            ' avoid an infinite Loop With the i != 1 check.
            If i <> 1 And find_my_factors Mod i = 0 Then
                found_prime_factors.Add(i)
                ' STEP 2:
                find_my_factors = find_my_factors / i
                ' STEP 3:
                Return onlyPrimeFactors()
            End If

            i += 1
        Loop

        found_prime_factors.Add(find_my_factors)
        Return found_prime_factors

    End Function

End Class

Main module code.

Module Arithmetic_PrimeFactors

    Sub Main()

        ' Use the list factors Class
        Dim test_guy = 48
        Dim prime_factors As New PrimeFactors
        prime_factors._init_(test_guy)
        Dim answer = prime_factors.onlyPrimeFactors()

        Console.WriteLine("Prime factorising " & test_guy & " gives:")
        Console.WriteLine(String.Join(" X ", answer))

    End Sub

End Module

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