Basic Calculator

[Duckegg]

Hi All,
I'm very new to VB and hope you wont mind me asking what may seem a silly question to most of you.

I am trying to create a form that adds two text boxes together, I have achieved this however when running the program if you forget to enter numbers in both boxes the program crashes!

I dont want to display an error message i just want the program to ignore empty boxes.

Is this easily achieved?

Regards
Chris

[Duckegg]

This is the 'button code' I have written so far


Dim x As Integer = Val(TextBox1.Text)
Dim y As Integer = Val(TextBox2.Text)


Mortage = TextBox1.Text
Insurance = TextBox2.Text

Label4.Text = Mortage + Insurance

[kleinma]

Why are you converting the strings in the textbox in the first 2 lines of code when you don't bother to use the x and y again to do your math?

Also, val returns a type double, so you are trying to do a narrowing conversion by converting the result of the VAL(textbox.text) method and squeezing a double type into an integer. Integers are only whole numbers, so if your insurance was 100.50, you would lose the decimal information.

Try this:

         Dim Mortage As Double = Val(TextBox1.Text)
        Dim Insurance As Double = Val(TextBox2.Text)

        Label4.Text = (Mortage + Insurance).ToString("0.00")

This also does look like it is school work right? Tell your teacher you should be coding with option strict on, which wouldn't let you try to force doubles into integers in the first place.

[Duckegg]

Hi kleinma,

I can understand you assuming it is school work, however it isnt, im just a real Newbie and i am trying to learn.

You reply is excellent and works really well,

I really feel like I have learnt something.

Regards
Chris

[kleinma]

well in that case tell yourself you should be coding with option strict on

Seriously though, by turning on this feature, the IDE will force you to make sure conversions between types are done explicitly, so there is less chance of obscure bugs (like dropping of decimal places) or runtime errors (like you were seeing).

Glad to hear it is working for you now.

[FourBlades]

A little more info:

If you turned option strict on, you no doubt immediately became the target of an intelligent IDE giving you messages that seemed to be quite a pain.

As Kleinma pointed out, with option strict on you have to overtly make the conversion. The IDE won't stop bothering you until you do. Why?

The reason is that this: The IDE is basically pointing out the possible loss of accuracy (or other problems) to you. This gives you the chance to basically "reply" with "yes, I know I'm doing that. I've considered the ramifications of doing so, and I'm certain this is what I want to do. Thank you, IDE, for telling me about that potential problem."

There may be other reasons that I'm not at the moment considering.

[stateofidleness]

also think about using lowercase variable names as well. Don't think it's set in stone anywhere, but seems to be "rule of thumb".

Constants all uppercase
variables use "camel casing"
Functions/Procedures and Classes use Uppercase first letter

this is from what I've seen with working with OOP so far.

[FourBlades]

Actually he had the casing standard correct.

It's parameters that are lower case:

Public Sub SomeSub(Byval parameter1 as Integer, Byval parameter2 as String)

Dim LocalInteger as Integer = parameter1
Dim LocalString as String = parameter2
'Although you'd probably not set param1 and 2 to the local CamelCase variables
'like that because they were passed by Value.

End Sub

Public Function SomeFunction(Byval first as Textbox, Byval second as MyType) As Thing
End Function

In this case Mortgage and Insurance are correctly written.

[FourBlades]

However the OP's variables x and y should have been X and Y.

Another standard for lower case is in looping variables.

For i as integer...
For each i as integer...

[stateofidleness]

so local variables are Upper and class level are lower?

[FourBlades]

Honestly?

Anyone can do as they please.
This only comes into play when you anticipate that one day someone else may have to read your code. That's when a standard comes in.

Hmmm...

If the name, whatever it is, can be used "stand alone" then capitalize and make camel case.

If the name, whatever it is, is found as a parameter then the first word would be lowercase and the second Proper; or if the name was just one word then lowercase.

If the name is part of any counter, then lower if one word; else lower then upper camel if two words.

In a class:
If the name is a backing field then lower.
If the name is a property, then upper and camel.
If the name is anything else in a class then upper and camel.


Whether it is Local or Class level does not matter.

Some examples:

Dim PeopleCounter as Integer...

For Each person as Person in People...
For Each fastCar as Car in Vehicles...

...(Byval one as Integer)...
...(Byval moreThanOne as String)...
Private Function NameOfFunction (...) as Boolean
Public Sub NameOfSub(...

If NameOfFunction Then
End If

You can probably find the recommendations on MSDN