[RESOLVED] What is wrong with this?

I am BRAND new to programming so please be gentle

I have been working on a calculator of sorts and things are finally progressing but I am encountering two errors that I cannot figure out.

1. If I run the calculator and I fill in both of the text boxes (listing price and sales price) then no errors are encountered, however, if I do not fill in one of the textboxes with a value then I receive:

"An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll

Additional information: Input string was not in a correct format."

With the error directing to which ever textbox value was left blank. It also says that the code has called into another function and when that function is finished, this is the next function that will be executed.

Here is the code for converting the two text boxes:

VB Code:

Public Function ListFees() As Double
 
 
        '   Compute the initial ebay listing fee
        '   based on the listing price of the item
 
        
 
        listprice = Double.Parse(TextBox1.Text)  'convert input string to number
 
 
 
        Select Case listprice
            Case 0.0
                list = 0.0
            Case 0.01 To 0.99
                list = 0.25
            Case 1 To 9.99
                list = (0.35)
            Case 10 To 49.99
                list = (0.6)
            Case 50 To 199.99
                list = 2.4
            Case 200 To 499.99
                list = 3.6
            Case Is >= 500
                list = 4.8
        End Select
 
 
 
 
    End Function
    Function FinalValue() As Double
 
        '   compute final value fee
        '   based on the sales price
 
 
        sellprice = Double.Parse(TextBox2.Text)
 
        Select Case sellprice
 
            Case 0 To 25
                fvfee = (sellprice * 0.0525)
            Case 25.01 To 1000
                fvfee = (sellprice - 25) * 0.0275 + 1.31
            Case Is > 1000
                fvfee = (sellprice - 1000) * 0.015 + 28.12
        End Select
 
    End Function

All variables have previously been declared as Double

2. The second problem is that when the program does run correctly, the decimals are all out of whack. I want all numbers to appear in a currency type of format (two places afer the decimal) but I am getting three or four, unless the second character is a zero, then I only get one digit after the decimal. I am sure I am missing a conversion or something?

Thanks in advance for any help

Alright, typical that as soon as I ask for help, I get it to work. Can anyone tell me if this a proper way to remedy the problem or if I just kind of rigged it to work?



Plus I still need help with the decimal place proble please.




New code is just the If..Else clause:

VB Code:

Public Function ListFees() As Double
 
 
        '   Compute the initial ebay listing fee
        '   based on the listing price of the item
 
        If IsNumeric(TextBox1.Text) = False Then
            list = 0.0
        Else
 
 
        listprice = Double.Parse(TextBox1.Text)  'convert input string to number
 
 
 
        Select Case listprice
            Case 0.0
                list = 0.0
            Case 0.01 To 0.99
                list = 0.25
            Case 1 To 9.99
                list = (0.35)
            Case 10 To 49.99
                list = (0.6)
            Case 50 To 199.99
                list = 2.4
            Case 200 To 499.99
                list = 3.6
            Case Is >= 500
                list = 4.8
        End Select
        End If
 
 
 
    End Function
    Function FinalValue() As Double
 
        '   compute final value fee
        '   based on the sales price
        If IsNumeric(TextBox2.Text) = False Then
            list = 0.0
        Else
 
 
            sellprice = Double.Parse(TextBox2.Text)
 
            Select Case sellprice
 
                Case 0 To 25
                    fvfee = (sellprice * 0.0525)
                Case 25.01 To 1000
                    fvfee = (sellprice - 25) * 0.0275 + 1.31
                Case Is > 1000
                    fvfee = (sellprice - 1000) * 0.015 + 28.12
            End Select
        End If
 
    End Function

Thanks

1. Trying to convert an empty string to a double will throw an exception as it is not a valid format. You can check yourself whether the TextBox is empty but this still doesn't account for the user entering invalid data, like letters. If you are not validating each character as it is entered then I suggest this: check whether the field is empty. If it is then do nothing. If it is not, use Double.TryParse to attempt to convert the text to a Double and display an error message if it fails.

VB Code:

Private Function DoSomething() As Double
        Dim listPrice As Double
 
        If Me.TextBox1.Text.Trim() = String.Empty Then
            'Do nothing or assume zero as you prefer.
            Return 0
        ElseIf Not Double.TryParse(Me.TextBox1.Text.Trim(), Globalization.NumberStyles.Any, Nothing, listPrice) Then
            'Display appropriate error message.
            Return 0
        End If
 
        'Use listPrice here, which has been populated in the call to TryParse.
    End Function

2. If you are dealing in currency then you should be using the Decimal data type as much as possible. This reduces the risk of round-off error due to floating point arithmetic. Unfortunately you have to use Double in some places because you need to use Double.TryParse. .NET 2.0 has added a Decimal.TryParse method but for now you're stuck with Double. If you want to convert a numerical value to currency, I suggest you use ToString("c"). This will automatically round to the standard number of decimal places for the local currency. I strongly suggest that you accept the default number of decimal places even if there are no cents. Consistency is a good thing. If you remove the cents then the user is not to know whether there are none or you just chose to remove them. If you do want remove the cents when there are none you could use logic like this:

VB Code:

Dim myDecimal As Decimal
        Dim myCurrencyString As String
 
        If myDecimal Mod 1 = 0 Then
            'Display no decimal places.
            myCurrencyString = myDecimal.ToString("c0")
        Else
            'Display the standard number of decimal places.
            myCurrencyString = myDecimal.ToString("c")
        End If

Edit:
IsNumeric is a valid method of validation but I, and others, prefer to avoid VB Runtime functions if possible.

Thanks for the very detailed response. I will take a few minutes to digest what you said and then try to implement it.

jm,

I implemented the first part of your post and it worked flawlessly, but I am having problems with the decimal part of your post. It seems that no matter where I try to convert a double to a decimal as you suggested, I get parse errors?

I've got a fair idea what the problem is but show me the code you are using so I can be specific.

jm,

Your assistance is more extremely appreciated, you will note that I actually have not implemented your first suggestion yet either because after further testing, I must have implemented it incorrectly b/c it was failing. The entire project is enclosed in zip.

I'm not a big one for downloading entire projects. Please just post the relevant section of the actual code, i.e. as text in a post.

Sorry, here it is:

VB Code:

Dim listprice As Double = 0    '   ebay listing price of item
    Dim sellprice As Double = 0    '   ebay selling price of item
    Dim shipprice As Double = 0    '   shipping fee charged for item
    Dim list As Double = 0         '   fee charged by ebay for listing item based on price
    Dim fvfee As Double = 0        '   final value fee charged by ebay based on the sales price
    Dim option1 As Double = 0      '   option1-4 are add on's to the listing fee for upgraded listing
    Dim option2 As Double = 0      '
    Dim option3 As Double = 0      '
    Dim option4 As Double = 0      '
    Dim paypalfee As Double = 0    '   fee charged by paypal if used
    Dim reserve As Double = 0      '   additional fee for a reserve price
 
 
   
 
 
 
    Public Function ListFees() As Double
 
 
        '   Compute the initial ebay listing fee
        '   based on the listing price of the item
 
        If IsNumeric(TextBox1.Text) = False Then
            list = 0.0
        Else
 
 
            listprice = Double.Parse(TextBox1.Text)  'convert input string to number
 
 
 
            Select Case listprice
                Case 0.0
                    list = 0.0
                Case 0.01 To 0.99
                    list = 0.25
                Case 1 To 9.99
                    list = (0.35)
                Case 10 To 49.99
                    list = (0.6)
                Case 50 To 199.99
                    list = 2.4
                Case 200 To 499.99
                    list = 3.6
                Case Is >= 500
                    list = 4.8
        End Select
 
        End If
 
 
    End Function
    Public Function reservefee() As Double
 
        If IsNumeric(TextBox4.Text) = False Then
            reserve = 0.0
        Else
 
 
            reserve = Double.Parse(TextBox4.Text)  'convert input string to number
 
 
 
            Select Case reservefee
                Case 0.0
                    reserve = 0.0
                Case 0.01 To 49.99
                    reserve = 1.0
                Case 50 To 199.99
                    reserve = 2.0
                Case Is > 200
                    reserve = Double.Parse(TextBox4.Text) * 0.01
            End Select
        End If
    End Function
 
    Function FinalValue() As Double
 
        '   compute final value fee
        '   based on the sales price
        If IsNumeric(TextBox2.Text) = False Then
            list = 0.0
        Else
 
 
            sellprice = Double.Parse(TextBox2.Text)
 
            Select Case sellprice
 
                Case 0 To 25
                    fvfee = (sellprice * 0.0525)
                Case 25.01 To 1000
                    fvfee = (sellprice - 25) * 0.0275 + 1.31
                Case Is > 1000
                    fvfee = (sellprice - 1000) * 0.015 + 28.12
        End Select
        End If
 
    End Function
 
 
 
 
    Function Options() As Double
 
        '   This section will compute the numeric value of each selected listing option
        '   each respective value is stored in the variable "option"
        '   followed by the box number (ie, option1 for combobox1
 
 
        '   compute the numeric value of each option selection combo1
 
 
 
        Select Case ComboBox1.Text
            Case "Select"
                option1 = 0
            Case "Gallery Picture"
                option1 = 0.35
            Case "Listing Designer"
                option1 = 0.1
            Case "Item Subtitle"
                option1 = 0.5
            Case "Bold"
                option1 = 1
            Case "10 Day Auction"
                option1 = 0.4
            Case "Gift Service"
                option1 = 0.25
            Case "Border"
                option1 = 3
            Case "Highlight"
                option1 = 5
            Case "Featured Plus"
                option1 = 19.95
            Case "Gallery Featured"
                option1 = 19.95
            Case "Home Page Featured"
                option1 = 39.95
            Case "Scheduled Listing"
                option1 = 0.1
        End Select
 
 
        '   compute the numeric value of each selection combo2
 
 
 
 
        Select Case ComboBox2.Text
            Case "Select"
                option2 = 0
            Case "Gallery Picture"
                option2 = 0.35
            Case "Listing Designer"
                option2 = 0.1
            Case "Item Subtitle"
                option2 = 0.5
            Case "Bold"
                option2 = 1
            Case "10 Day Auction"
                option2 = 0.4
            Case "Gift Service"
                option2 = 0.25
            Case "Border"
                option2 = 3
            Case "Highlight"
                option2 = 5
            Case "Featured Plus"
                option2 = 19.95
            Case "Gallery Featured"
                option2 = 19.95
            Case "Home Page Featured"
                option2 = 39.95
            Case "Scheduled Listing"
                option2 = 0.1
        End Select
 
        '   compute the numeric value of each selection combo3
 
 
 
        Select Case ComboBox3.Text
            Case "Select"
                option3 = 0
            Case "Gallery Picture"
                option3 = 0.35
            Case "Listing Designer"
                option3 = 0.1
            Case "Item Subtitle"
                option3 = 0.5
            Case "Bold"
                option3 = 1
            Case "10 Day Auction"
                option3 = 0.4
            Case "Gift Service"
                option3 = 0.25
            Case "Border"
                option3 = 3
            Case "Highlight"
                option3 = 5
            Case "Featured Plus"
                option3 = 19.95
            Case "Gallery Featured"
                option3 = 19.95
            Case "Home Page Featured"
                option3 = 39.95
            Case "Scheduled Listing"
                option3 = 0.1
        End Select
 
 
        '   compute the numeric value of each selection combo4
 
 
 
 
        Select Case ComboBox4.Text
            Case "Select"
                option4 = 0
            Case "Gallery Picture"
                option4 = 0.35
            Case "Listing Designer"
                option4 = 0.1
            Case "Item Subtitle"
                option4 = 0.5
            Case "Bold"
                option4 = 1
            Case "10 Day Auction"
                option4 = 0.4
            Case "Gift Service"
                option4 = 0.25
            Case "Border"
                option4 = 3
            Case "Highlight"
                option4 = 5
            Case "Featured Plus"
                option4 = 19.95
            Case "Gallery Featured"
                option4 = 19.95
            Case "Home Page Featured"
                option4 = 39.95
            Case "Scheduled Listing"
                option4 = 0.1
        End Select
 
 
 
 
 
    End Function
    Public Function PaypalFees() As Double
        If IsNumeric(TextBox2.Text) = False Then
            paypalfee = 0.0
        Else
 
            paypalfee = (sellprice + shipprice) * 0.029 + 0.3
        End If
    End Function

God only knows what else you may find wrong :)

I thought you were talking about the decimal places in the currency.

I was suggesting that you declare the relevant variables as Decimal and only convert to Double if and when you have to, like this:

VB Code:

'Double.TryParse only accepts a Double.
Dim myDouble As Double
 
If Double.TryParse(Me.TextBox1.Text, Globalization.NumberStyles.Any, Nothing, myDouble) Then
    'Convert the parsed Double value to a Decimal for use.
    Dim myDecimal As Decimal = CDec(myDouble)
Else
    MessageBox.Show("Please enter a valid number.")
End If

This is only a simple example so you would need to adapt it to your needs.

Not sure if I completely understand what you are suggesting, but i will continue to mess with it. I guess the only way I will learn is to fall down ALOT.

Thank you

I'm suggesting that all the variables that you have declared as Double should be declared as Decimal instead. You don't have to do this but, as I said, it protects you from round-off errors that can occur in floating-point arithmetic, i.e. with Singles and Doubles. You would use Decimal types everywhere except where it was not possible, like the fourth argument to Double.TryParse. In that situation you would have to pass it a Double variable and then convert the Double to a Decimal, e.g. by using CDec, before using it. That way you perform no arithmetic with the Double so you cannot get round-off errors.

I get what you are saying, the problem I have, because I am pretty clueless, is implementing it. I have studied your examples and I have tried to do something similar in my project, but it's not pretty.

I am really just guessing with it all b/c I do not have enough grasp of all the terminology involved yet. I have been reading and viewing videos on this subject night and day, but it seems like no one actually teaches what you need to know.

I apologize for my lack of knowledge, but I seriously am trying, I just don't get what actually needs to be changed.

You don't need to apologise for not having experience. The only way to get it is to do. I do try to use the correct terminology as much as I'm able, which can be a little confusing if you haven't heard it before. Just keep on trying and learn from your mistakes. That's what I did and I'm sure everyone else here is the same. At least you do have places like this to get help. My best advice to you is to not be shy about using the help system provided by the IDE. That's where I've learned the majority of what I know. It can be a little confusing or incomplete at times, so then there's places like this, but the help system should always be your first port of call. You should have worn out your F1 button within the month. :)

Thanks for all your help jm