CODEWITHSUNDEEP
vb.netvisual-studio-2010
user1239333
user1239333

Reputation: 85

Conversion from string "" to type 'Double' is not valid

This function keeps giving me problem I cannot seem to find the right combination to get it working. I am trying to apply discount if certain amount is reached but I keep getting conversion error. What do I need to do so I define everything so it works?

Function coupon() As Decimal

        Dim decdiscount As Decimal
        Dim inta, intb, intc As Decimal

        inta = 20.0
        intb = 40.0
        intc = 60.0

        If lblSubtotal.Text > inta Then
            decdiscount = 0.05
        End If


        If lblSubtotal.Text > intb Then
            decdiscount = 0.1
        End If


        If lblSubtotal.Text > intc Then
            decdiscount = 0.2
        End If

        Return decdiscount
    End Function

Upvotes: 1

Views: 3787

Answers (4)

Mark Hall
Mark Hall

Reputation: 54552

You really should enable Option Strict for your projects. It would help you avoid the conversion error at runtime by letting you know that you had an implicit conversion when you entered it. You could then use the Decimal.TryParse Method as BluesRockAddict and Andrew Kennan suggest.

From above link:

When you set Option Strict to On, Visual Basic checks that data types are specified for all programming elements. Data types can be specified explicitly, or specified by using local type inference. Specifying data types for all your programming elements is recommended, for the following reasons:

  • It enables IntelliSense support for your variables and parameters. This enables you to see their properties and other members as you
    type code.
  • It enables the compiler to perform type checking. Type checking helps you find statements that can fail at run time because of type conversion errors. It also identifies calls to methods on objects
    that do not support those methods.
  • It speeds up the execution of code. One reason for this is that if you do not specify a data type for a programming element, the Visual
    Basic compiler assigns it the Object type. Compiled code might have
    to convert back and forth between Object and other data types, which
    reduces performance.

In your case it would flag the implicit conversions in your code.

Upvotes: 2

COLD TOLD
COLD TOLD

Reputation: 13599

you need to convert you string to decimal you cant compare string to decimal like this

  If System.Convert.ToDecimal(lblSubtotal.Text) > inta Then
            decdiscount = 0.05
        End If

Upvotes: 0

Andrew Kennan
Andrew Kennan

Reputation: 14157

I expect the value of lblSubtotal.Text is not a number. Perhaps try something like this:

Dim subTotal as Decimal
If Not Decimal.TryParse(lblSubTotal.Text, subTotal) Then
' Throw an exception or something
End If

If subTotal > inta Then
...

Upvotes: 0

BluesRockAddict
BluesRockAddict

Reputation: 15683

You should use Decimal.Parse() or Decimal.TryParse(), for example:

If Decimal.Parse(lblSubtotal.Text) > inta Then
    decdiscount = 0.05
End If

or

Dim subTotal As Decimal = Decimal.Parse(lblSubtotal.Text, Globalization.NumberStyles.AllowDecimalPoint)

If subTotal > inta Then
    decdiscount = 0.05
End If

Upvotes: 1

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