This is assuming an input of two integers: a lower limit and an upper limit. And the code will capture any prime numbers between the two.

Dim lowerLimit, upperLimit, primeNumber As Integer Dim isPrime As Boolean = False lowerLimit = CType(TextBox1.Text, Integer) upperLimit = CType(TextBox2.Text, Integer) While lowerLimit < upperLimit primeNumber = lowerLimit If primeNumber = 2 Or primeNumber = 3 Then isPrime = True ElseIf primeNumber = 1 Then isPrime = False ElseIf primeNumber = upperLimit Then Exit While Else For i As Integer = 2 To (primeNumber - 1) If primeNumber Mod i = 0 Then isPrime = False Exit For Else isPrime = True End If Next End If If isPrime = True Then TextBox3.Text += primeNumber & vbCrLf End If lowerLimit += 1 End While

As you can see, I used two textboxes for the lower and upper limit values and then when I found a prime number, I output it to a third multiline textbox. I skipped over 1-3 as one is of course not a prime number and then two and three do not fit well into the for loop with values. Which is why I started the for loop at 2 and looped up to the upperlimit minus 1. This is, of course, because a number is always divisible by 1 and itself (the definition of a prime number). If the loop ever catches a number that is divisble by another number with a 0 remainder it flags the number as non-prime and exits the loop. Otherwise it will continue looping through until it reaches one less than the upper limit.

Hope this helps someone out there.