Newbie: Error in mod evaluation

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juneappal - 02 Nov 2005 06:18 GMT

Sorry to pester the list with this - it is such a simple problem I
can't figure out what to search for.

This is m first day of playing with Java. I notice that

> System.out.println((34/5.0)%1);

evaluates as:

0.7999999999999998

Why is that?

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Andrew Thompson - 02 Nov 2005 06:44 GMT

> Sorry to pester the list ..

usenet newsgroup (specifically). A 'list' generally refers to
a mailing-list, which this is not.

>..with this - it is such a simple problem I
> can't figure out what to search for.
>
> This is m first day of playing with Java.

I think you'll have a lot of fun. Quick note. A better
group for those just starting in Java/programming is
<http://www.physci.org/codes/javafaq.jsp#cljh>

Though it makes good sense to continue *reading* c.l.j.programmer.

>>System.out.println((34/5.0)%1);

...

> 0.7999999999999998

The machine representation of floating point numbers is
inherently inaccurate. It is the saem for all programming
languages. The simple fix for Java is to apply a
NumberFormat or DecimalFormat to the output.
<http://java.sun.com/j2se/1.5.0/docs/api/java/text/DecimalFormat.html>
<http://java.sun.com/j2se/1.5.0/docs/api/java/text/NumberFormat.html>

HTH

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Roedy Green - 02 Nov 2005 07:11 GMT

>This is m first day of playing with Java. I notice that
>
[quoted text clipped - 5 lines]
>
>Why is that?

See http://mindprod.com/jgloss/floatingpoint.html

Are you sure you meant %?? % is an integer operator.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Roedy Green - 02 Nov 2005 07:18 GMT

On Wed, 02 Nov 2005 06:11:09 GMT, Roedy Green
<my_email_is_posted_on_my_website@munged.invalid> wrote, quoted or
indirectly quoted someone who said :

>Are you sure you meant %?? % is an integer operator.

% is defined for floating point but I think every production use I
have ever seen of it was on ints.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Thomas Schodt - 02 Nov 2005 11:45 GMT

> % is defined for floating point

As described here
<http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#239829>

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Roedy Green - 02 Nov 2005 12:06 GMT

On Wed, 02 Nov 2005 10:45:52 +0000, Thomas Schodt
<spamtrap@xenoc.demon.co.uk.invalid> wrote, quoted or indirectly
quoted someone who said :

>> % is defined for floating point
>
>As described here
><http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#239829>

quoting from the Java glossary which in turn quotes from the JLS:
http://mindprod.com/jgloss/modulus.html

% is also defined to work with float and double operands, though that
use is quite rare.

The result of a floating-point remainder operation as computed by the
% operator is not the same as that produced by the remainder operation
defined by the IEEE 754 floating point standard. The IEEE 754
remainder operation computes the remainder from a rounding division,
not a truncating division. % on floating-point operations behaves
analogously to the integer remainder operator; this may be compared
with the C library function fmod. The IEEE 754 remainder operation may
be computed by the library routine Math. IEEEremainder. (Note the
violation of the naming conventions.)

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Newbie: Error in mod evaluation

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