Resetting a variable value after it is returned by a method?

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3.50/5 (2 votes)

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I'm in my first C# class and the professor is MIA, please help.

I'm working on a simple "cash register" program from the text book that totals the cost of services at an auto mechanic. I got it to calculate all of the correct totals and clear the form, but the values that were returned when I click the "calculate" button remain for all of the check-box items. What do I have to do differently to reset those variables back to 0?

here is a sample of my code:

C#

//The OilLubeCharges method returns the total charges for an oil
//change and/or a lube job, if any.
private double OilLubeCharges(out double lubeSubTotal)
{
    if (oilChangeCheckBox.Checked == true)
    {
        oilChangeCost = 26;
    }

    if (lubeJobCheckBox.Checked == true)
    {
        lubeJobCost = 18;
    }

    return lubeSubTotal = oilChangeCost + lubeJobCost;

}

//ClearOilLube method clears any checked boxes and total values in the Oil & Lube group
private void ClearOilLube()
{
    oilChangeCheckBox.Checked = false;
    lubeJobCheckBox.Checked = false;
}

//ClearLubeSubTotal clears any values set to the group's variable
private double ClearLubeSubTotal(out double lubeSubTotal)
{
    return lubeSubTotal = 0;
}

Even after this ClearLubeSubTotal method is called, the value remains and with nothing checked, if I click "calculate" the total keeps giving me the old value, not 0.

Any help will be greatly appreciated!

Posted 10-Apr-14 7:23am

JeannineJ

Updated 10-Apr-14 7:37am

Richard MacCutchan

v4

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Comments

Sergey Alexandrovich Kryukov 10-Apr-14 12:41pm

Why, why do you use "out" parameter? (Yes, this is a valuable opportunity, but why in this case?) Why not ref?
—SA

Richard MacCutchan 10-Apr-14 12:43pm

you have not shown the code where you call these methods so it's difficult to figure out what is going wrong. But, as Sergey asks, why are you using out parameters when you are returning the value from your methods?

Maciej Los 10-Apr-14 14:19pm

I gave you a 5 stars, because i believe there is something more than simple: "how to reset value"?
Please see my comment to the Solution1 by Sergey Alexandrovich Kryukov.

2 solutions

Solution 1

The question is just the absurd. If you want to reset the value to 0, why do you set it to oilChangeCost + lubeJobCost? It should mean that you don't need zero, you need some other value. Probably, you need zero later. Then just do it. ClearLubeSubTotal does not make much sense, how it's better than just lubeSubTotal = 0?

The whole idea to use out is questionable, if not totally bad. First of all, in your usage, it should be ref. Hope you can read about it and see what' s the difference. But the whole idea of using by-reference mechanism is quite wrong. You do two different things: assign the value to the field and return value. The clear way to do it in safer and cleaner way is to remove "out". The call will always do some assignment then.

—SA

Posted 10-Apr-14 7:47am

Sergey Alexandrovich Kryukov

Comments

Maciej Los 10-Apr-14 13:39pm

Maestro, i like when you say that way: The question is just the absurd.

Sergey Alexandrovich Kryukov 10-Apr-14 13:57pm

Thank you Maciej.
Even though I'm not sure that OP would like it...
—SA

Maciej Los 10-Apr-14 14:12pm

In some cases a bucket of cold water on the head is necessary ;)
By the way: is there any method to call custom event handler after property get method was called.
For example:

class StupidClass
{
    private int sv =0;
    public  event PropertyGetEventHandler PropertyGet;
    int StupidProperty
    {
        get{
            return sv;
            //here event handler call is not accesible ;(
            OnPropertyChanged(myValue);            
           }
    }

    protected void OnPropertyGet(int value)
    {
        PropertyGetEventHandler handler = PropertyGet;
        if (handler != null)
        {
            handler(this, new PropertyGetEventArgs(value));
        }
    }
}

Sergey Alexandrovich Kryukov 10-Apr-14 14:35pm

If an event is declared in the same class (exact same class, not base class, not anything else), you can call Invoke on it. Why?
—SA

Maciej Los 10-Apr-14 14:48pm

I thought about OP's question in a different manner ;) Please, see my comment to the question.
Invoke... OK, but at this moment i can't imagine how it could be realised... via delegates?

Sergey Alexandrovich Kryukov 10-Apr-14 15:44pm

And what's the use? Do you mean that you want to reset a property to zero just after it is set to zero? Why?
—SA

Maciej Los 10-Apr-14 16:00pm

Yeah, possible usage is to reset value to zero, but i can imagine many other usages. For example: i'm a software developer and i'm developing software on shareware rules. User can runs application (or specific command only) 30 times. I would like to communicate to user how many "runs" left him. But do not limit yourself to this. It's just an example.
Do not understand me wrong. I don't need instructions, i need to understand how to realise that (invoke event). Via delegates? Am i right or am i wrong?

Sergey Alexandrovich Kryukov 10-Apr-14 16:15pm

Say, PropertyGet.Invoke(this, new PropertyGetEventHandler(/*...*/)); ... :-)
—SA

Sergey Alexandrovich Kryukov 10-Apr-14 16:17pm

...and don't forget to check up:

if (PropertyGet != null)
PropertyGet.Invoke(...);

Will be interesting if you explain why resetting a value... :-)

—SA

Maciej Los 10-Apr-14 17:18pm

Hmmm... Sorry, but we misunderstand each other - i think. Main problem is: how to call event hadler after return SomeValue; inside get{} property. As far as i know, any code after return word is not reachable for compiler. Am i more clear now? Please, see my second comment one more time.

Sergey Alexandrovich Kryukov 10-Apr-14 18:28pm

Okay, don't mix up event handler and the event instance. Event handler belongs to the user of the class with an event instance. This user can make is a named method (I mean, not anonymous, or anonymous, but stored in a delegate), then this method or delegate instance can be simply called, without any relationship to the event. The difference? Event instance can be multicast, so other handlers won't be called, only one will.

And the event handler can be invoked, the way I've shown above. This can be done only in the code of the declaring class, but this will call all the handlers added to the invocation list of this event instance.

I guess, there is nothing else, so I described all you can "call". Now you choose. :-)

—SA

Maciej Los 11-Apr-14 1:30am

Got it!

Maciej Los 10-Apr-14 17:21pm

Of course, i can call event handler before property returns any value:

get{
//here is possible to call eventhandler 
return value;
//but here any code is not reachable ;(
}

Maciej Los 10-Apr-14 17:23pm

Who down-voted this answer? It's valuable answer, even if some one doesn't see it!

Sergey Alexandrovich Kryukov 10-Apr-14 18:24pm

It happens these days, some high-reputation member, maybe the same one...
Doesn't matter; I up-voted Solution 2, for the common sense... (we say more precisely "здравый смысл", "healthy sense/meaning"... ("zdrowy rozsądek"?))
—SA

Maciej Los 11-Apr-14 1:31am

Zdrowy rozsądek - this is it!

Sergey Alexandrovich Kryukov 11-Apr-14 1:41am

We also have similar word "рассудок", the modern usage of it is a bit old-styled; "в здравом рассудке" refers to a person in sanity: alert, not sleeping, not under intoxication and not insane.
—SA

Maciej Los 11-Apr-14 1:44am

I believe both of us are this kind of persons ;)

Sergey Alexandrovich Kryukov 11-Apr-14 1:47am

I really hope... :-)
—SA

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ZurdoDev · Accepted Answer · 2014-04-10T09:36:00

Solution 2

You haven't shown all of your code so I will assume that lubeSubTotal, oilChangeCost, and lubeJobCost are global variables. All you need to do is in your ClearOilLube() method set each varible to 0.

C#

lubeSubTotal = 0;
oilChangeCost = 0;
lubeJobCost = 0;

or, you can actually do it in 1 step, which I don't prefer because of readability:

C#

lubeSubTotal = oilChangeCost = lubeJobCost = 0;

It's read right to left. The assignment of 0 goes into lubeJobCost and that is assigned to oilChangeCost, etc.

Posted 10-Apr-14 9:36am

ZurdoDev

Comments

Sergey Alexandrovich Kryukov 10-Apr-14 18:19pm

Short and to the point, without artificial complications, a 5.

By the way, it maybe a bit late, but... did you see my 1st of April publication?
Power Over IP: Testing of the First Experimental Facility.

Hope it can feel you more energetic :-) and fun; and perhaps you can ask me some difficult questions. ;-)

—SA

JeannineJ 11-Apr-14 19:31pm

That did it! I just included my variables IN my method, instead of making them global. Thanks RyanDev. Like I said, this is my first time using C# and I have NO help, at all. My college should be paying you instead of my instructor. ;)

-Jeannine

ZurdoDev 11-Apr-14 21:19pm

No problem. I'll send them a bill. :)

Resetting a variable value after it is returned by a method?

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