Need some help with VB (prime numbers and factors)

[pinnacle2009]

I am trying to get a VB program that will determine whether or not a user-generated number is prime or not. Right now, all I have is this:

Dim num As Integer
        Dim factor As Integer
        factor = 1
        num = TextBox1.Text
        Do While num >= factor
            If num Mod factor = 0 Then
                RichTextBox1.AppendText(vbCrLf & factor)
            End If
            factor = factor + 1
        Loop

It's just getting the factors of a number. I cannot get it to tell prime numbers apart, however. Any help?

 

[pinnacle2009]

Okay, after looking and and searching, I now have:

Dim num As Integer
        Dim i As Integer
        Dim counter As Integer
        num = TextBox1.Text
        counter = 0
        i = 1
        Do While i <= num
            If num Mod i = 0 Then
                counter = counter + 1
            End If
            i = i + 1
        Loop
        If counter = 2 Then
            TextBox2.Text = "This is a prime number!"
        Else
            TextBox2.Text = "This is NOT a Prime number!"
        End If

However, I don't know what the counter does exactly.. (part of this was copied)

Could someone explain?

 

[kyeana]

Here is a hint, the defination of a prime number is a number that can be divided by one and itself. Go through the code line by line and see if you can't understand what it is doing.

 

[pinnacle2009]

got it now. we actually just did stuff with it in class today.