Re: How come I get a rounded number when I multiply doubles?? - C# Discussion Boards

Re: How come I get a rounded number when I multiply doubles??

Theraot28-Jul-10 4:15

28-Jul-10 4:15

According to ECMA-334 9.4.4.3 Real literals Paragraph 2:
"If no real-type-suffix is specified, the type of the real literal is double."*

*: in ECMA-334 9.4.4.3 a grammar form that excludes any number without a real-type-suffix or decimal-digits after the dot to be a real literal.

If you are on a non ECMA compilant implementation of C#, move to another compiler/interpreter.

Re: How come I get a rounded number when I multiply doubles??

pinskerr28-Jul-10 1:10

pinskerr

28-Jul-10 1:10

Your other respondents are right that InvItem.Price appears to be an integer, so you would expect the answer to be 24.0.

However you say the answer is 12.0, that is really weird - is that what you meant?

Re: How come I get a rounded number when I multiply doubles??

roman_s28-Jul-10 3:43

roman_s

28-Jul-10 3:43

Sorry there is a mathematical mistake what I needed to know is when dividing an integer with a remainder I was getting
double variable(2425) / 100 would give you 24.0 , I was wondering why I wasn't getting 24.25

solution was because I was dividing an integer into another integer,
I corrected this simply by multiplying 100.00 instead of 100

Re: How come I get a rounded number when I multiply doubles??

ely_bob28-Jul-10 3:43

ely_bob

28-Jul-10 3:43

I've run into this problem Many times... You need to explicitly tell the compiler what type you want from each operation

dbRecipeTotal = (double)(((double)(RI.Quantity / dbRecipeTotalQuantity)) * ((double)(InvItem.Price / 100)));

this will make sure that you are always in the precision your looking for, indepentant of whether you use a lower precision numeral type.

I'd blame it on the Brain farts.. But let's be honest, it really is more like a Methane factory between my ears some days then it is anything else...

Re: How come I get a rounded number when I multiply doubles??

Charvak Karpe28-Jul-10 4:12

Charvak Karpe

28-Jul-10 4:12

ely_bob wrote:
dbRecipeTotal = (double)(((double)(RI.Quantity / dbRecipeTotalQuantity)) * ((double)(InvItem.Price / 100)));
this will make sure that you are always in the precision your looking for, indepentant of whether you use a lower precision numeral type.

ely_bob, your solution still doesn't work because (InvItem.Price / 100) will be 24, so ((double)(InvItem.Price / 100)) will be 24.0

It needs to be ((double)InvItem.Price / 100). I didn't cast the 100 to double because when one of the arguments to operator/ is a double, the other one is automatically cast (I think).

Re: How come I get a rounded number when I multiply doubles??

ely_bob28-Jul-10 4:32

ely_bob

28-Jul-10 4:32

Yeah your right.. you need to be more liberal with your (double)'s....

That just goes to show you.. don't post before coffee.... Laugh | :laugh:

I'd blame it on the Brain farts.. But let's be honest, it really is more like a Methane factory between my ears some days then it is anything else...

Re: How come I get a rounded number when I multiply doubles??

Member 315345731-Jul-10 18:13

Member 3153457

31-Jul-10 18:13

double Quantity = 28.88887;
double dbRecipeTotalQuantity = 28.88887;
int Price = 2425;
double dbRecipeTotal = (Quantity / dbRecipeTotalQuantity) * (Price / 100.0);

Re: How come I get a rounded number when I multiply doubles??

Kenneth Kasajian28-Jul-10 8:29

Kenneth Kasajian

28-Jul-10 8:29

A floating point number can never be specified exactly in memory, unless the number is an even power of two.

If you just ignore the division part of your example. Even if you were to type:

Even if you were type:

dbRecipeTotal = 24.25;

It may display as 24.25 or 24.0 or 24.24999999999999 depending on how print formating is specified.

Just remember, you're never going to store 24.25 in a floating point number exactly.

ken@kasajian.com / www.kasajian.com

Re: How come I get a rounded number when I multiply doubles??

PaulLinton28-Jul-10 14:15

PaulLinton

28-Jul-10 14:15

You are always going to store 24.25 in a floating point number exactly. 24.25 is a power of two. You should never see any of the results you listed (except 24.25) no matter what print formatting is specified.

Re: How come I get a rounded number when I multiply doubles??

Kenneth Kasajian28-Jul-10 14:42

Kenneth Kasajian

28-Jul-10 14:42

Thanks.

I wasn't aware that 24.25 is an even power of two. Learn something new every day.

ken@kasajian.com / www.kasajian.com

Re: How come I get a rounded number when I multiply doubles??

Mitch Hughes29-Jul-10 11:04

Mitch Hughes

29-Jul-10 11:04

[Stepping on my soapbox]
When dealing with floating point numbers, you should never assume that a number will be stored exactly. While some numbers can be stored exactly, most will not be.

From the cases I have encountered, too many people assume that a floating point number is good enough for exact numerical needs. But if the value 24.24999999999999 instead of 24.25 would be considered incorrect in your application, you should not be using floating point values.

Time and time again I have been called in to analyze why dollar values were coming in off by a penny or two (or more), and it has always* boiled down to the choice of using floating point representation to store exact values.

* Since 1992 I have encountered only 2 instances where the problem was an actual bug in the library.

Re: How come I get a rounded number when I multiply doubles??

sushantpokharel28-Jul-10 20:46

sushantpokharel

28-Jul-10 20:46

The answer lies in the way implicit data type conversion works. Dividing and integer by and integer will never yeild a float or a double. So, InvItem.Price / 100 becomes 24 and not 24.25. I'm sure you understand the rest. To get correct answer do something like

<pre>( InvItem.Price / 100.0 ) * ( RI.Quantity / dbRecipeTotalQuantity )</pre>

Re: How come I get a rounded number when I multiply doubles??

Member 315345731-Jul-10 18:08

Member 3153457

31-Jul-10 18:08

I think InvItem.Price is int so 2425/100=24
you can write : InvItem.Price/100.0 to get correct result

Re: How come I get a rounded number when I multiply doubles??

Member 315345731-Jul-10 18:12

Member 3153457

31-Jul-10 18:12

I think InvItem.Price is int so 2425/100=24
you can write : InvItem.Price/100.0 to get correct result:
(this is tested and returns correct result):
double Quantity = 28.88887;
double dbRecipeTotalQuantity = 28.88887;
int Price = 2425;
double dbRecipeTotal = (Quantity / dbRecipeTotalQuantity) * (Price / 100.0);

Re: How come I get a rounded number when I multiply doubles??

kxal8-Aug-10 18:25

kxal

8-Aug-10 18:25

I think the InvItem.Price is an integer,if so,the division will diacard the
part after decimal point automatically.

using telerik schedule

mrkeivan27-Jul-10 3:54

mrkeivan

27-Jul-10 3:54

Hi, I'm trying to convert string to recurrence rule object, In the web forms it's done using the following code:

string rruleAsString = "Sample";
RecurrenceRule parsedRule;
RecurrenceRule.TryParse(rruleAsString, out parsedRule);
appointment.RecurrenceRule = parsedRule;

but in winforms it doesn't support "TryParse" !!!
please help me out

Thanx
K

Re: using telerik schedule

Wes Aday27-Jul-10 4:10

Wes Aday

27-Jul-10 4:10

mrkeivan wrote:
winforms it doesn't support "TryParse"

And what did telerik tell you when you asked them?

Why is common sense not common?
Never argue with an idiot. They will drag you down to their level where they are an expert.
Sometimes it takes a lot of work to be lazy
Individuality is fine, as long as we do it together - F. Burns

Re: using telerik schedule

mrkeivan27-Jul-10 19:33

mrkeivan

27-Jul-10 19:33

They suggested webform (I guess i didn't mention that I needed winform function)
anyway, I found it, the same function in a differenct class can be used here,

using Telerik.WinControls.UI.Scheduler.ICalendar;
CalHelper.TryParseRecurrenceRule(rruleAsString, out parsedRule);

Quick Linq to XML question

xkrja27-Jul-10 3:05

xkrja

27-Jul-10 3:05

I'm starting out with linq to xml and have a quick question:

I have the following xml-file:

<countries>
<country code="AF" iso="4">Afghanistan</country>
<country code="AL" iso="8">Albania</country>
<country code="DZ" iso="12">Algeria</country>
<country code="AS" iso="16">American Samoa</country>
<country code="AD" iso="20">Andorra</country>
.
.
.

How can I get a result containing all the country names by using a linq expression? I tried the following but it only gives me "Afghanistan":

XDocument xmlDoc = XDocument.Load("countries.xml");

var countries = from country in xmlDoc.Descendants("countries")
select new
{
Name = country.Element("country").Value,
};

Thanks for help!

Re: Quick Linq to XML question

Chris Trelawny-Ross27-Jul-10 5:26

Chris Trelawny-Ross

27-Jul-10 5:26

Your Linq query is asking for the wrong thing from the XDocument.

The Descendents() method returns descendents of the object (in this case, the XDocument) which have the specified name (in this case 'countries'). So it is yielding a single enumerable element (because your XML Document has only one <countries> element).

What you really need is to get the 'country' descendents of the XDocument: from xmlDoc.Descendents("country") and then just get the Value property of the elements of the enumeration. Here's some code that works for you:

var countries = from country in xmlDoc.Descendants("country")
    select new
    {
        Name = country.Value
    };

Re: Quick Linq to XML question

souidi abderrahman27-Jul-10 21:47

souidi abderrahman

27-Jul-10 21:47

Can you get a list of country: Smile | :)

 <br />
XDocument xmlDoc = XDocument.Load("countries.xml");<br />
        <br />
        List<string> countries = from country in xmlDoc.Descendants("country")<br />
                        select new<br />
                        {<br />
                            Name = country.Value,<br />
                        };<br />

Fetch the content of a website

Krishna Varadharajan27-Jul-10 1:55

Krishna Varadharajan

27-Jul-10 1:55

Hi,

How can i fetch the content of a website using c# (windows app). Purpose is to upload in our search engine.

Thanx

krishna

Re: Fetch the content of a website

Peace ON27-Jul-10 2:17

Peace ON

27-Jul-10 2:17

For search engine, you only need to read meta tags.
Here is nice video[^] for the same.

Also find following links useful.

http://www.codeasp.net/blogs/teisenhauer/microsoft-net/170/parse-meta-tags-in-c-sharp[^]

HTH

Jinal Desai - LIVE
Experience is mother of sage....

Re: Fetch the content of a website

Krishna Varadharajan27-Jul-10 2:47

Krishna Varadharajan

27-Jul-10 2:47

Hi,

Thanks for your info. what you said is true, only meta tag is enough... but in some situation we wont get i hope....for example type following tag in google "times of india sports" from that result check the third link "More Sports - Sports - The Times of India" which is the current updation of the website ...... how we can get those current updation results which is not mention in meta-tag. Even i may be wrong clear my doubt pls.

Thanks

krishna

Re: Fetch the content of a website

Peace ON27-Jul-10 2:53

Peace ON

27-Jul-10 2:53

For such situation, I think you need to search html for required information.
Once you have complete html of website you can easily search any content within it.

For that you need to do "Screen Scraping"[^].
Find following link useful for the same.

http://www.codersource.net/microsoft-net/c-advanced/html-screen-scraping-in-c.aspx[^]

HTH

Jinal Desai - LIVE
Experience is mother of sage....

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