Prime Number Generator

[bplus]

Here's one of many of mine:

Code: (Select All)

_Title " A Simple Prime Sieve and Factor of 4 Digit Numbers" ' mod  2024-12-27 bplus

' sieving marks composites ONLY, primes are what is left when composites are crossed off

DefLng A-Z

topN = 9999 '  any 4 digit number

Dim ff(topN) '     need array to hold numbers crossed off, ff stands for first (prime) factor

For pcandidate = 2 To topN '       absolutely no optimation here!!!!

    If ff(pcandidate) = 0 Then '   this is next prime discovered so cross off all composites

        For i = pcandidate * pcandidate To topN Step pcandidate ' check all multiples of pcand

            If ff(i) = 0 Then ff(i) = pcandidate ' going to use ff to factor numbers

        Next

    End If

Next

For i = 2 To topN

    If ff(i) = 0 Then c = c + 1

Next

Print c; " prime numbers 2 to 9999."

Do

    Input "Enter a 4 digit number to factor or see if prime ", n

    m = n

    While ff(m)

        Print ff(m);

        m = m / ff(m)

    Wend

    If m = n Then Print n; "is prime." Else Print m

Loop Until n < 2

EDITED to do something useful with our calculations!