Programming Forums - For Loops And Variables

Public Function primechk(max As Integer)
I'm still writing the prime number algorithm and so far I have this code for my function:

Dim primes() As Integer

ReDim primes(0)

primes(0) = 2

For x = 3 To max

  bound = UBound(primes)

  For index = 0 To bound

    If x Mod primes(index) = 0 Then

      Exit For

    End If

    indices = index

  Next index

  If indices = bound Then

    ReDim Preserve primes(bound + 1)

    primes(bound + 1) = x

  End If

  

Next x

  Print primes(bound)

End Function

It works fine, but I'm still optimizing, before I was using this:

For index = 0 To bound

    If x Mod primes(index) = 0 Then

      Exit For

    End If

    If index = bound Then

       ReDim Preserve primes(bound + 1)

       primes(bound + 1) = x

    End If

Next index

But I realized that checking the index each iteration was very inefficient, so I decided to put the If then statement outside the embeded for loop:

Next index

  If index = bound Then

    ReDim Preserve primes(bound + 1)

    primes(bound + 1) = x

  End If

  

Next x

Unfortunately, the program was not working... After a quick print test with the variable index, I came to the realization that it was destroyed as soon as the loop exited. So I decided to use the sligtly more efficient

For index = 0 To bound

    If x Mod primes(index) = 0 Then

      Exit For

    End If

    indices = index

  Next index

It's deffinetly better than repeating the if then and comparisons. But I still feel that the assignment is taking up too much time. In order to make this program truly optimized I want to reuse index.

How do I keep the variable index from being destroyed after the loop is exited so I can reuse its value later?

Thanks!