Solved

Perl precision arithmetic, typcasting?

Posted on 2011-03-09
4
575 Views
Last Modified: 2013-12-25
Thinking out loud here... just need some assurance and explanation.

I ran across code like this today.

$number = 100.12;
$number = int($number*100);
print "$number\n";
$number = $number/100;
print "$number\n";

Yields:
10012
100.12

as expected....

The problem: 1200.12
Yields:
120011
1200.11

So I think the only issue is the int(). I removed it and so far results are as expected. I'm just surprised that I found this issue, the code has been in use for a long time. So I'm concerned that there was a good reason for it and I'm creating another unforeseen problem. Also, want to make sure there's just not a better way to do it.

The value should always be a whole dollar or dollar.cents value, and should be enforced as such. Then stored without the decimal.

So (I guess) my question is what would you do?

The objective is to store the number without the decimal in it. The code snip is just an adhoc example. I mean you could do it without even using math. I know Perl has issues with floating-point arithmetic precision.
 
0
Comment
Question by:kindaprog
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
4 Comments
 
LVL 9

Expert Comment

by:Subrat (C++ windows/Linux)
ID: 35089897
What about using the string?
0
 

Author Comment

by:kindaprog
ID: 35089938
Do you mean just checking if it has a decimal point?

Then if it does split on it and make sure the right side has two digits (add a zero if needed etc.) and cat the two parts back together... if it doesn't just tack on two zeros.
0
 
LVL 48

Accepted Solution

by:
Tintin earned 500 total points
ID: 35090118
Perl doesn't have an issue with floating point.  It's common to all programming languages.

int EXPR
       int     Returns the integer portion of EXPR.  If EXPR is omitted, uses
               $_.  You should not use this function for rounding: one because
               it truncates towards 0, and two because machine representations
               of floating point numbers can sometimes produce
               counterintuitive results.  For example, "int(-6.725/0.025)"
               produces -268 rather than the correct -269; that's because it's
               really more like -268.99999999999994315658 instead.  Usually,
               the "sprintf", "printf", or the "POSIX::floor" and
               "POSIX::ceil" functions will serve you better than will int().
0
 

Author Comment

by:kindaprog
ID: 35090442
Yes Sir. I was just realizing this fact. Same results in a c program...

Do you have a preference/recommendation??

I was just trying this and it seems to work consistently.

$number = sprintf("%.0f", $number)

Thank you.
0

Featured Post

On Demand Webinar: Networking for the Cloud Era

Ready to improve network connectivity? Watch this webinar to learn how SD-WANs and a one-click instant connect tool can boost provisions, deployment, and management of your cloud connection.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

A year or so back I was asked to have a play with MongoDB; within half an hour I had downloaded (http://www.mongodb.org/downloads),  installed and started the daemon, and had a console window open. After an hour or two of playing at the command …
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
In this seventh video of the Xpdf series, we discuss and demonstrate the PDFfonts utility, which lists all the fonts used in a PDF file. It does this via a command line interface, making it suitable for use in programs, scripts, batch files — any pl…
Video by: Mark
This lesson goes over how to construct ordered and unordered lists and how to create hyperlinks.

628 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question