CalculateRetail

    Function ValidateInput(inPut As Object) As Boolean

        If IsNumeric(inPut) Then
            Return inPut > 0
        Else
            Return False
        End If

    End Function

    Function CalculateRetail(WholesaleCost As Decimal, MarkUppercentage As Integer) As Decimal
        ' calculate the retail price
        Return WholesaleCost * ((MarkUppercentage / 100) + 1)
    End Function

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ' Validate user inpout

        If Not ValidateInput(wholesale.Text) Then
            System.Windows.Forms.MessageBox.Show("Please enter a valid Retail Price")
            Exit Sub
        End If
        If Not ValidateInput(markup.Text) Then
            System.Windows.Forms.MessageBox.Show("Please enter a positive MarkUp Percentage 1 - 100")
            Exit Sub
        End If
        ' Calculate Retail Price
        Label1.Text = "$" & CalculateRetail(wholesale.Text, markup.Text)
    End Sub