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Rounding Decimal value get wrong result


Rounding Decimal value get wrong result

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ada.xi
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hi all,

I try to give a expression to round some filed like below,
Round(Fields!unit_price.Value, Fields!Dom_Price_Places.Value)
---- Fields!unit_price.Value(decimal(18,8))
----Fields!Dom_Price_Places.Value(tinyint)
now I run into a one Fields!unit_price.Value=2.34500000, Fields!Dom_Price_Places.Value=2
What I get is
Round(CDec("2.34500000"), 2) return 2.34.

Round(2.34500000, 2) return 2.35

What's the difference here?
Is this a bug?

And help would be appreciated. Thanks,
ada.xi
ada.xi
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Any Help? thanks
Lynn Pettis
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ada.xi (1/25/2011)
hi all,

I try to give a expression to round some filed like below,
Round(Fields!unit_price.Value, Fields!Dom_Price_Places.Value)
---- Fields!unit_price.Value(decimal(18,8))
----Fields!Dom_Price_Places.Value(tinyint)
now I run into a one Fields!unit_price.Value=2.34500000, Fields!Dom_Price_Places.Value=2
What I get is
Round(CDec("2.34500000"), 2) return 2.34.

Round(2.34500000, 2) return 2.35

What's the difference here?
Is this a bug?

And help would be appreciated. Thanks,




What is CDec? I can't find it in BOL anywhere.

My guess, CDec is converting "2.34500000" to 2.34, not 2.345.

Cool
Lynn Pettis

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ada.xi
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Cdec ---Convert to Decimal.

And (CDec("2.34500000")=2.34500000) return true.
Lynn Pettis
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ada.xi (1/25/2011)
Cdec ---Convert to Decimal.



In what? As I said, I can't find it anywhere in Books Online.

Cool
Lynn Pettis

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Lynn Pettis (1/25/2011)
ada.xi (1/25/2011)
Cdec ---Convert to Decimal.



In what? As I said, I can't find it anywhere in Books Online.


Nevermind, I found it in the Visual Studio Help System, it is a VB function.

Cool
Lynn Pettis

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Daniel Bowlin
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You say that
Round(CDec("2.34500000"), 2) return 2.34.

but it should be
Round(2.34500000, 2) return 2.35


What happens when the number is 2.35500000 does it return
2.35 or 2.36?

If it returns 2.36 you are encountering something called banker's rounding where a 5 will round up to an even number, but a 5 will round down if the round up number is odd. In other words the 5 will alway round in the direction of the even number whether that is up or down.

Without the long explanation of why banker's rounding exists, most people just code around it by testing the digit they are rounding and if it is a 5 they will add a value of 1 to that digit to make sure it rounds up.

Hope this helps.
Doug Lane
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Daniel Bowlin (1/27/2011)

If it returns 2.36 you are encountering something called banker's rounding where a 5 will round up to an even number, but a 5 will round down if the round up number is odd. In other words the 5 will alway round in the direction of the even number whether that is up or down.

I think the use of CDec is invoking the bankers rounding somehow. Try dropping that function if you can; maybe put the rounding in the query if that's possible.

For what it's worth, here's something more from MSDN:
When the fractional part is exactly 0.5, CInt and CLng always round it to the nearest even number. For example, 0.5 rounds to 0 and 1.5 rounds to 2. CInt and CLng differ from the Fix and Int functions, which truncate, rather than round, the fractional part of a number. Also, Fix and Int always return a value of the same type as is passed in.

Though it doesn't include CDec in that list, I wouldn't be surprised if it behaves like CInt and CLng.
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