Public Function IsPrime(number As Integer) As Boolean
If number = 2 Then
Return True
End If
If number Mod 2 = 0 OrElse number < 2 Then
'no even numbers except 2 is a prime and 1 is by definition not a prime
Return False
End If
Dim sqr As Integer = CInt(Math.Ceiling(Math.Sqrt(number)))
'We can skip all even numbers in the loop since only even numbers are evenly divisible with
'another even number and those aren't prime numbers
For i = 3 To sqr Step 2
If number Mod i = 0 Then
'Have a divisor, not a prime
Return False
End If
Next
Return True
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim lowerLimit, upperLimit, primeNumber, i As Integer
Dim isPrime As Boolean = False
Integer.TryParse(TextBox1.Text, lowerLimit)
Integer.TryParse(TextBox2.Text, upperLimit)
Do While lowerLimit < upperLimit
primeNumber = lowerLimit
TextBox3.Text +=
?????????????????????? & vbCrLf
lowerLimit += 1
Loop
End Sub
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