solutions + demos

Class Str
    Private str As String
    Sub New(str As String)
        Me.str = str
    End Sub
    Sub setString(str As String)
        Me.str = str
    End Sub
    Sub printString()
        Console.WriteLine(str.ToUpper())
    End Sub
End Class

Class Rectangle
    Private length As Decimal
    Private width As Decimal
    Sub New(length As Integer, width As Integer)
        Me.length = length
        Me.width = width
    End Sub
    Function getArea()
        Return length * width
    End Function
End Class

Class Circle
    Private radius As Decimal
    Sub New(radius As Decimal)
        Me.radius = radius
    End Sub
    Function getArea()
        Return 3.14 * radius * radius
    End Function
    Function getCircumference()
        Return 2 * 3.14 * radius
    End Function
End Class

Class Operation
    Private a As Integer
    Private b As Integer
    Sub New(a As Integer, b As Integer)
        Me.a = a
        Me.b = b
    End Sub
    Function power()
        Dim multTotal As Integer = 1
        For i = 1 To b
            multTotal *= a
        Next
        Return multTotal
    End Function
End Class

Class Customer
    Private customerNumber As Integer
    Private customerName As String
    Private price, qty, discount, totalPrice, netPrice As Integer
    'note, all currency in lowest denomination (eg cents)
    'to prevent floating point rounding error
    Sub New(customerNumber As Integer, customerName As String)
        Me.customerNumber = customerNumber
        Me.customerName = customerName
        qty = 0
        price = 0
        discount = 0
        totalPrice = 0
        netPrice = 0
    End Sub
    Sub calDiscount()
        totalPrice = price * qty
        If totalPrice >= 50000 Then
            discount = totalPrice * 25 * 0.01
        ElseIf totalPrice >= 25000 Then
            discount = totalPrice * 15 * 0.01
        Else
            discount = totalPrice * 10 * 0.01
        End If
        netPrice = totalPrice - discount
    End Sub
    Sub input(price, qty)
        Me.price = price
        Me.qty = qty
        calDiscount()
    End Sub
    Sub show()
        Console.WriteLine("Customer number: " & customerNumber)
        Console.WriteLine("Customr name: " & customerName)
        Console.WriteLine("Total price: " & totalPrice)
        Console.WriteLine("Discount: " & discount)
        Console.WriteLine("Net price: " & netPrice)
    End Sub
End Class

Sub Main()
    Dim name As Str = New Str("Taufiq")
    name.printString()
    Dim rectangle As Rectangle = New Rectangle(3, 4)
    Console.WriteLine(rectangle.getArea())
    Dim circle As Circle = New Circle(5)
    Console.WriteLine(circle.getArea)
    Console.WriteLine(circle.getCircumference)
    Dim func As Operation = New Operation(2, 3)
    Console.WriteLine(func.power())
    Dim customer As New Customer(12, "Taufiq")
    customer.input(200, 5)
    customer.show()
    Console.ReadLine()
End Sub