Private Sub cmdFindPrimes_Click()
Dim is_prime() As Boolean
Dim max_number As Long
Dim i As Long
Dim j As Long
Dim txt As String

    Screen.MousePointer = vbHourglass
    
    ' Create the array.
    max_number = CLng(txtMaxNumber.Text)
    ReDim is_prime(2 To max_number)
    For i = 2 To max_number
        is_prime(i) = True
    Next i

    For i = 2 To max_number \ 2
        If is_prime(i) Then
            ' Cross out all numbers that are
            ' multiples of this one.
            For j = 2 To max_number \ i
                is_prime(j * i) = False
            Next j
        End If
    Next i
    
    ' Display the primes.
    j = 0
    For i = 2 To max_number
        If is_prime(i) Then
            txt = txt & Format$(i, "@@@@@@@")
            j = j + 1
            If (j Mod 5) = 0 Then txt = txt & vbCrLf
        End If
    Next i
    txtPrimes.Text = txt

    Screen.MousePointer = vbDefault
End Sub