Create/call functions, use TryParse

Question

I am building a calculator for an auto repair shop (homework assignment) and I have to use create a function/call a function and use a Try Parse method.

Any tips/suggestions. Here are my variables :

Private dblOilChange As Double = 36.0
Private dblLubeJob As Double = 26.0
Private dblRadiatorFlush As Double = 50.0
Private dblTransmissionFlush As Double = 120.0
Private dblInspection As Double = 15.0
Private dblReplaceMuffler As Double = 200.0
Private dblTireRotation As Double = 20.0
Private dblParts As Double
Private dbltxtBoxParts As Double
Private dbltxtBoxLabor As Double
Private intTotal As Integer 

Thank you in advance,

Regards,

Hector B.

Answer 1

This uses Nullable Value Types

    Private Function ToDouble(strVal As String) As Double?  
        ' Nullable Value Types  
        ' https://learn.microsoft.com/en-us/dotnet/visual-basic/programming-guide/language-features/data-types/nullable-value-types  
        Dim rv As Double?  
        Dim d As Double  
        If Double.TryParse(strVal, d) Then  
            rv = d  
        End If  
        Return rv  
    End Function  
  

To use it

        Dim TheVal As Double  
        Dim valid As Double?  
        valid = ToDouble("ABD")  
        If valid.HasValue Then TheVal = valid.Value  
        valid = ToDouble("123.456")  
        If valid.HasValue Then TheVal = valid.Value