Need some help with VB (prime numbers and factors)

pinnacle2009

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Feb 15, 2010
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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:

Code:
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

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Feb 15, 2010
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Okay, after looking and and searching, I now have:

Code:
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

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May 21, 2008
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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.