Debugging Classes

[pisotmo]

Hi guys. I'm doing a program that will calculate the new price. Iv been using a class to put my code their. Iv been getting errors in my form code.

Heres the class code

Public Class Computer
    Private _id As String
    Private _price As Decimal

    Public Property Id() As String
        Get
            Return _id
        End Get
        Set(ByVal value As String)

        End Set
    End Property

    Public Property Price() As Decimal
        Get
            Return _price
        End Get
        Set(ByVal value As Decimal)

        End Set
    End Property

    Public Sub New()
        _id = String.Empty
        _price = 0D
    End Sub

    Public Sub New(ByVal model As String, ByVal cost As Decimal)
        Id = model
        Price = cost
    End Sub

    Public Function CalcNewPrice(ByVal discountPercent As Decimal) As Decimal
        Return _price - _price * discountPercent / 100
    End Function

Here's my form code

        Dim computerPurchased As New Computer
        Dim isConverted As Boolean
        Dim rate As Decimal
        Dim newPrice As Decimal

        isConverted = Decimal.TryParse(origTextBox.Text, Computer.Price)
        If isConverted Then
            Computer.Id = modelTextBox.Text
            rate = Convert.ToDecimal(discountListBox.SelectedItem.ToString.TrimEnd("%"c))
            newPrice = Computer.CalcNewPrice(rate)
            newLabel.Text = newPrice.ToString("C2")
        Else
            MessageBox.Show("The cost must be numeric.", "Computer Workshop", _
                MessageBoxButtons.OK, MessageBoxIcon.Information)
        End If
    End Sub

the error is in the Computer.Price , Computer.CalcNewPrice and Computer.ID
it says Reference to a non-shared member requires an object reference.

[jmcilhinney]

You're trying to access an instance member via the class itself rather than an instance of the class. Here:

Dim computerPurchased As New Computer

you're creating a new instance of the Computer class and assigning it to the 'computerPurchased' variable. To access members of that instance you use the variable, not the class.

[pisotmo]

So what should I do? thanks!

[jmcilhinney]

Use the 'computerPurchased' variable to access those members rather than the Computer class, as I said.

[pisotmo]

Thanks, I actually did that. But for some reason my application won't work as expected.
I couldnt get the outcome of the new price.

Is there something wrong with these?

newPrice = Computer.CalcNewPrice(rate)

Public Function CalcNewPrice(ByVal discountPercent As Decimal) As Decimal
        Return _price - _price * discountPercent / 100
    End Function

I need to calculate the new price

[gep13]

Hey,

I don't think you are getting what John is saying. Try the following:

        Dim computerPurchased As New Computer
        Dim isConverted As Boolean
        Dim rate As Decimal
        Dim newPrice As Decimal

        isConverted = Decimal.TryParse(origTextBox.Text, computerPurchased.Price)
        If isConverted Then
            computerPurchased.Id = modelTextBox.Text
            rate = Convert.ToDecimal(discountListBox.SelectedItem.ToString.TrimEnd("%"c))
            newPrice = computerPurchased.CalcNewPrice(rate)
            newLabel.Text = newPrice.ToString("C2")
        Else
            MessageBox.Show("The cost must be numeric.", "Computer Workshop", _
                MessageBoxButtons.OK, MessageBoxIcon.Information)
        End If
    End Sub

Gary

[pisotmo]

Thanks Gary, I actually did that but it didnt compute for the new price.
It always shows an output of $0.00

[jmcilhinney]

I actually did that

Nothing you posted implied that, and the code you posted implied the opposite.

It always shows an output of $0.00

Then you need to actually debug. Debugging does not consist of simply reading the code looking for errors. It involves running the code and watching it in action, seeing what path execution follows and the values of your variables along the way. Put a break point on the top of the code and then step through it line by line, using F10 and F11, and make sure that execution takes the path you expect and your variables contain the values you expect. As soon as something you don't expect happens, you've found a problem.

[gep13]

Agreed.

You are going to need to step through the code, and figure out exactly what is going on.

Are you familiar with how to debug your application? i.e. setting breakpoints, using Asserts, setting watch variables, etc?

Gary