Vista - Re: HELP: 5.01 - 5 = 9.9????

06-11-2009

PadovaBoy (ovvero Giovanni) schrieb:

Quote:

> Hi at all.
> I have a "curious" problem with Asp classic (vbscript engine) in IIS6 (ms
> server 2003) ad IIS7 (ms vista):
>
> This is the test:
>
> dim a,b
> a = CDbl(5.01)
> b = CDbl(5.00)
> Response.Write a & " - "&b&" = "& ( a - b) & "<br>"
> c = CDbl ( a - b) 'another try..
> Response.Write c & "<br>"
>
> The results are:
> 5,01 - 5 = 9,99999999999979E-03
> 9,99999999999979E-03
>
> Why? At my home 5.01 - 5 = 0.01 not 9,9...
>
> Tnx for any suggestions..
>
>

Two problems:

(1) the computer's numbers are different from the mathematical concept
of numbers. See (e.g.)

http://en.wikipedia.org/wiki/Floating_point

for the how and why. In your case the exact result 0.01 is approximated
by 9,99999999999979 * 10 ^ -3.

(2) use FormatNumber if you want to display numbers to the user

Quote:

>> a = 5.01 : b = 5.0
>> wscript.echo typename(a), typename(b), a, b, a-b, formatnumber(a-b,6)
>>

Double Double 5,01 5 9,99999999999979E-03 0,010000

Quote:

>> wscript.echo 9.9 * 10 ^-3
>>

0,0099

Quote:

>> quit

06-11-2009	#1 (permalink)
ekkehard.horner n/a posts	Re: HELP: 5.01 - 5 = 9.9???? PadovaBoy (ovvero Giovanni) schrieb: Quote: > Hi at all. > I have a "curious" problem with Asp classic (vbscript engine) in IIS6 (ms > server 2003) ad IIS7 (ms vista): > > This is the test: > > dim a,b > a = CDbl(5.01) > b = CDbl(5.00) > Response.Write a & " - "&b&" = "& ( a - b) & "<br>" > c = CDbl ( a - b) 'another try.. > Response.Write c & "<br>" > > The results are: > 5,01 - 5 = 9,99999999999979E-03 > 9,99999999999979E-03 > > Why? At my home 5.01 - 5 = 0.01 not 9,9... > > Tnx for any suggestions.. > > Two problems: (1) the computer's numbers are different from the mathematical concept of numbers. See (e.g.) http://en.wikipedia.org/wiki/Floating_point for the how and why. In your case the exact result 0.01 is approximated by 9,99999999999979 * 10 ^ -3. (2) use FormatNumber if you want to display numbers to the user Quote: Quote: >> a = 5.01 : b = 5.0 >> wscript.echo typename(a), typename(b), a, b, a-b, formatnumber(a-b,6) >> Double Double 5,01 5 9,99999999999979E-03 0,010000 Quote: Quote: >> wscript.echo 9.9 * 10 ^-3 >> 0,0099 Quote: Quote: >> quit
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