VBA – Function to write the divisors of a number

Yesterday I wrote an article for an Excel function, checking whether a specified number is prime or not.

Today I tought that it would be somehow a good idea to modify this function, in a way to check the number and if it is not prime to write down the divisors. Actually it was not very tough, as far as I have changed only a few lines of the code, making it a lot slower by removing the square root from the previous calculation. Anyway, the speed is not an issue, so enjoy the result from the routine “TestPrimeNumbers()” here:

The way the function works can be viewed here:

And finally the code. Find the 10 differences with the one from yesterday :

Option Explicit

Public Const cPrime As String = "Prime"
Public Const cNotPrime As String = "Not a prime, has other divisors."
Public Const cNotPositive As String = "A number should be an integer bigger than 0."

Public Function fDivisors(lNumber) As String

    Dim i As Long
    Dim bFirst As Boolean

    If (lNumber = 1) Or (lNumber = 2) Or (lNumber = 3) Then
        fDivisors = cPrime
        Exit Function
    End If

    If (lNumber < 1) Or (lNumber <> CLng(lNumber)) Then
        fDivisors = cNotPositive
        Exit Function
    End If

    For i = 2 To (lNumber + 1) / 2 Step 1
    
        If lNumber Mod i = 0 Then
            If Not bFirst Then
                fDivisors = i
            Else
                fDivisors = fDivisors & ", " & i
            End If
            bFirst = True
        End If
    Next i

    If Len(fDivisors) < 1 Then fDivisors = cPrime

End Function

Public Sub TestPrimeNumbers(lStart As Long, lEnd As Long)

    Dim i As Long

    For i = lStart To lEnd Step 1
        Debug.Print i & "  " & fDivisors(i)
    Next i

End Sub

Enjoy it! 🙂