To All,

I have found this nested For/Next loop designed to generate the prime numbers up to a certain number, in this case 13.

My question is why does the following code work as it is written? I have highlighted the portion in red that I don't understand. I could have generated this code myself but I would have written it with the red highlighted portion deleted, and by the way I find that the code works well with the red hightlighted portion present or deleted.

From my perspective, I don't understand why it would work with the hightlighted portion included, that is I don't understand why the final value of 13 would be included if the most that j could be is j-1 or 12. It would seem that you could never reach 13/13 or mod =0 for the final value of 13.

Any thoughts?

         For i = 3 To 13
            For j = 2 To i - 1
                If (i Mod j) = 0 Then
                    Exit For
                End If
            Next
            If (i = j) Then
                Console.Out.Write("{0} ", j)
            End If
        Next
        Console.Out.WriteLine()


Thank you for any insight,

Little Shell

every number is divisible by itself (result = 1) so there no need to test the number against itself. If you test it against itself, the condition (i mod j) is zero, therefore exiting the loop with value i=j (same as if you did not test against itself, in the case the loop never exits)

Marcostraf,

Thank you for your comments. You have been very helpful.

Little Shell