Prime or Composite

[Gulya]

Dear Access Forum Experts,



I have numbers starting 1 to 500,000,000,000 and would like to check/segregate them whether it’s Prime or Composite. So appreciate if somebody could provide me a solution.

thanks

[Minty]

Is this an assignment?

I ask because finding Primes is a classic College assignment and you wouldn't be wanting us to do your work for you would you... ?

[Gulya]

Is this an assignment?

I ask because finding Primes is a classic College assignment and you wouldn't be wanting us to do your work for you would you... ?

if it was an assignment, I would have easily solve with the following formula in excel (=IF(J4=2,"Prime",IF(AND(MOD(J4,ROW(INDIRECT("2:"& ROUNDUP(SQRT(J4),0))))<>0),"Prime","Composite"))

The reason I requested through AccessForum is that Excel is straggling to handle huge data.... and maybe there is an option in Access to segregate numbers (as mentioned below) faster without time consuming

Table:

Inventory	Prime/Composite
41022242542	Composite
41022242543	Composite
41022242544	Composite
41022242545	Composite

[Minty]

Just checking
I doubt if access will be much more efficient to be honest

This function will return a result and test it for you

Public Function fnIsPrime(lInput As Long) As Boolean
    Dim i As Long
    
    fnIsPrime = True
    If lInput = 1 Then
        fnIsPrime = False
        Exit Function
    End If
    For i = 2 To lInput - 1
        If lInput Mod i = 0 Then
            fnIsPrime = False
            Exit Function
        End If
    Next i
End Function


Sub testPrime()
    Dim lNumber As Long
    Dim sAns As Boolean
    Dim tTime As Date
    
    tTime = Now
    
    For lNumber = 1 To 10000
        sAns = fnIsPrime(lNumber)
        Debug.Print lNumber; sAns
    Next lNumber
    
    Debug.Print  tTime; Now
    
    
End Sub

It took 15 seconds to run the loop and display 10000 records.

You could probably speed it up by not checking even numbers, as they can't be a prime?

[Micron]

You could probably speed it up by not checking even numbers, as they can't be a prime?

The first test is division by 2 so it does that?

For i = 2 To lInput - 1
If lInput Mod i = 0 Then

EDIT - I guess you meant bypass them altogether, but the function call would have to test that. However, the code already tests that so I think you'd just be sort of replacing one test with another - except the current one is going to run anyway?

[Minty]

The first test is division by 2 so it does that?

For i = 2 To lInput - 1
If lInput Mod i = 0 Then

@Micron - Yes you are correct, it's a generic function.
What I meant to say and didn't put very eloquently was - don't pass them into the function in the first place.
e.g assuming you have a list of all your input numbers query it to only include the odd ones.

Even now I'm making a pigs ear of describing that...

[Micron]

I edited my post before I saw yours. I think what you have there is efficient enough. First, you'd have to figure out if a number is a prime and if so, remove it from your list. That would be doing what your function is designed to do for you, thus you wouldn't need the function? Without using the function, are you going to remove 421589 from that list? The answer is yes, by the way. If you did remove them all from your list, then you'd have only primes left.

[Minty]

I just changed the test routine to this and the time to execute went down to 2 seconds!
Improvements : only test the odd numbers and only print out the primes. The debug always has an overhead.

Sub testPrime()
    Dim lNumber As Long
    Dim sAns As Boolean
    Dim tTime As Date
    
    tTime = Now
    
    For lNumber = 1 To 10000 Step 2
        sAns = fnIsPrime(lNumber)
        If sAns = "true" Then Debug.Print lNumber; sAns
    Next lNumber
    
    Debug.Print Now; tTime
    
    
End Sub

[Gulya]

I just changed the test routine to this and the time to execute went down to 2 seconds!
Improvements : only test the odd numbers and only print out the primes. The debug always has an overhead.

Sub testPrime()
    Dim lNumber As Long
    Dim sAns As Boolean
    Dim tTime As Date
    
    tTime = Now
    
    For lNumber = 1 To 10000 Step 2
        sAns = fnIsPrime(lNumber)
        If sAns = "true" Then Debug.Print lNumber; sAns
    Next lNumber
    
    Debug.Print Now; tTime
    
    
End Sub

Thanks a lot Minty for the response, could you please share the template as i'm straggling to use the provided codes plz

[Minty]

There is no template just the code, and you will need to adjust the data types to LongLong to handle that size of number.

Also how did you expect to handle that volume of rows in excel?
At a million rows per spreadsheet you will need 500,000 spreadsheets (That is half a million! ) to handle the output from the routine.
Even running that on a healthy SQL server would take ages to generate the results and how would you store them, certainly not in Access.

So perhaps having piqued my interest you could explain what the real purpose of this question is? As what you are asking for and your premise for asking are still unclear.
By the way while testing I found 4,294,967,291 is a prime.

[Micron]

By the way while testing I found 4,294,967,291 is a prime.

What is the significance of that number?

[Minty]

What is the significance of that number?

Absolutely nothing that I am aware of. It was just a very big number and is a prime.

Unless of course...

You are a paid up member of the tin hat brigade