Function in VBA to give me prime number not working

Question

I tried this function to give me Prime Number but it ain't working. I can't think of anything. I can do this easily in JS but here it just gives me headache.

Function JeLiProst(N As Integer) As Boolean
If N = 0 Then JeLiProst = False
If N = 1 Then JeLiProst = False
If N = 2 Then JeLiProst = True
For I = 2 To N - 1
If N Mod I = 0 Then 
JeLiProst = False
Else
JeLiProst = True
End If
End Function

I haven't used vba in a million years but shouldn't you break the loop and exit the function with false as soon as `N Mod I = 0` is true? — Joakim Danielson, Mar 23 '20 at 08:39
Possible duplicate of [Prime number for n value](https://stackoverflow.com/questions/60098497/prime-number-for-n-value) — T.M., Mar 23 '20 at 09:07
@JoakimDanielson Honestly I tried doing this, ```For I = 2 To N - 1 If N Mod I = 0 Then GoTo Fal Next JeLiProst = True Fal: JeLiProst = False ``` Didnt do much, now not even if 2 = true condition work — DrexxBoban, Mar 23 '20 at 09:10
Either I or the community member who judged this to be a duplicate didn't understand the question. In my opinion the referenced "Duplicate" bears no similarity to this question whatsoever. I have posted an answer. Let the OP decide if it's useful. — Variatus, Mar 23 '20 at 09:26
@Variatus The OP believes that `JeLiProst = False` works like `return false` in javascript. Their key misconception is that this assignment exits the function. The duplicate question shows how it is not the case and what to do instead. The *purpose* of the function (to test for prime number) is not even relevant at that point. — GSerg, Mar 23 '20 at 11:38

score -2 · Answer 1 · answered Mar 23 '20 at 09:22

Does this function do what you want?

Function JeLiProst(N As Integer) As Boolean

    Dim Primes As Variant
    Dim i As Integer

    ' prime numbers below 50. Extend if required.
    Primes = Array(2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47)

    If N > 1 Then
        For i = 0 To UBound(Primes)
            If Primes(i) > N Then
                JeLiProst = True
                Exit For
            Else
                If (N Mod Primes(i)) = 0 Then
                    JeLiProst = (N = Primes(i))
                    Exit For
                End If
            End If
        Next i
        If i > UBound(Primes) Then
            MsgBox N & " appears to be a prime number but I lack" & vbCr & _
                   "the data to assert that as a definite fact." & vbCr & _
                   "I shall classify it as 'not prime'.", _
                   vbInformation, "Insufficient stored data"
        End If
    Else
        JeLiProst = True
    End If
End Function

Function in VBA to give me prime number not working

1 Answers1