Dim x As Integer
            Dim i As Integer
            Dim Flag As Boolean = False

            x = TextBox1.Text
            For i = 2 To x / 2
                If (i = x) Then i = i + 1
                If (x Mod i = 0) Then
                    Flag = True
                    Exit For
                End If
            Next

            If (Flag = False) Then
                ' this num is prime number
                MsgBox("PRIME")
            Else
                ' this num is not prime number
                MsgBox("NOT PRIME")
            End If