sprintf doesn't round correctly?

[Guest]

Hi, I have the following code, where the multiplication results in a
dollar amount which needs to be rounded to the nearest cent.

$a = sprintf("%.2f", 1900*18.12895);
print $a;

The multiplication yields the value 34445.005, which should be rounded
up to 34445.01, but perl says that $a has the value 34445.00. Why is
it exhibiting this behavior?

 

[Chris Haffenstedt]

Hi, I have the following code, where the multiplication results in a
dollar amount which needs to be rounded to the nearest cent.

$a = sprintf("%.2f", 1900*18.12895);
print $a;

The multiplication yields the value 34445.005, which should be rounded
up to 34445.01, but perl says that $a has the value 34445.00. Why is
it exhibiting this behavior?

sprintf doesn't round at all. In your example, you get the result of
your multiplication, and after that, sprintf gives you the result with
the two digits after the ".".
More about rounding in Perl:
http://www.perl.com/doc/FAQs/FAQ/oldfaq-html/Q4.13.html

 

[Guest]

sprintf doesn't round at all. In your example, you get the result of
your multiplication, and after that, sprintf gives you the result with
the two digits after the ".".
More about rounding in Perl:http://www.perl.com/doc/FAQs/FAQ/oldfaq-html/Q4.13.html

That is not true, because I tried this code:

$a = sprintf("%.2f", 3.0051);
print $a;

And it printed out 3.01

 

[Jürgen Exner]

Hi, I have the following code, where the multiplication results in a
dollar amount which needs to be rounded to the nearest cent.

$a = sprintf("%.2f", 1900*18.12895);
print $a;

The multiplication yields the value 34445.005,

No, it doesn't. At least not on a typical computer.

which should be rounded
up to 34445.01, but perl says that $a has the value 34445.00. Why is
it exhibiting this behavior?

You must have missed the introductory lesson in the Introduction into
Computer Numerics class.

Try
$a = sprintf("%.20f", 1900*18.12895);
print $a;
and the reason will become obvious (note: 2 replaced with 20 digits).

For a more detailed explanation please see 'perldoc -q 9999'.

jue

 

[Joost Diepenmaat]

Hi, I have the following code, where the multiplication results in a
dollar amount which needs to be rounded to the nearest cent.

$a = sprintf("%.2f", 1900*18.12895);
print $a;

The multiplication yields the value 34445.005, which should be rounded
up to 34445.01, but perl says that $a has the value 34445.00. Why is
it exhibiting this behavior?

The direction of rounding at exactly x.yx5 is debatable. Perl uses
banker's rounding, which rounds towards even:

printf("%1.0f",0.5) => "0"
printf("%1.0f",1.5) => "2"

There are good reasons why it does this for general rounding: the last
time we had this question it turned into a rediculously long discussion.

Just see http://en.wikipedia.org/wiki/Rounding

 

[Guest]

No, it doesn't. At least not on a typical computer.


You must have missed the introductory lesson in the Introduction into
Computer Numerics class.

Try
        $a = sprintf("%.20f", 1900*18.12895);
        print $a;
and the reason will become obvious (note: 2 replaced with 20 digits).

For a more detailed explanation please see 'perldoc -q 9999'.

jue

Ah, that explains it. Thanks.

 

[Jürgen Exner]

The direction of rounding at exactly x.yx5 is debatable. Perl uses
banker's rounding, which rounds towards even:

This may or may not be the case. Either way it is not the reason for the
OPs problem. He doesn't have a trailing '5' do being with.

jue

 

[Tim Greer]

Hi, I have the following code, where the multiplication results in a
dollar amount which needs to be rounded to the nearest cent.

$a = sprintf("%.2f", 1900*18.12895);
print $a;

The multiplication yields the value 34445.005, which should be rounded
up to 34445.01, but perl says that $a has the value 34445.00. Why is
it exhibiting this behavior?

See:

perldoc -q decimals

 

[Martien Verbruggen]

sprintf doesn't round at all.

sprintf and printf do rounding.

See

# perldoc -q round

and

# perldoc -f sprintf
(search for 'rounded')

Martien