RE: [PHP] Warning: Division by zero

[kyle.smith]

It's always better to validate your inputs in any was possible, this
helps prevent exploits. 

-Original Message-
From: Gary [mailto:gwp...@ptd.net] 
Sent: Thursday, April 30, 2009 8:51 AM
To: php-general@lists.php.net
Subject: [PHP] Warning: Division by zero

I have a script that is a result of data entered in a form

On the script (when I test without data entry), I am getting a warning
that
Warning: Division by zero in .inc.php on line 15.

The warning is correct, however the viewer cannot access the second
script without entering the data that would cancel the warning.

Is this something I should worry about? or would it be better to right
in an isset?

I'm sorry if this does not seem clear. 



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Re: [PHP] Warning: Division by zero

[Christoph Boget]

 I have a script that is a result of data entered in a form
 On the script (when I test without data entry), I am getting a warning that
 Warning: Division by zero in .inc.php on line 15.
 The warning is correct, however the viewer cannot access the second script
 without entering the data that would cancel the warning.
 Is this something I should worry about? or would it be better to right in an
 isset?

Well, just as a general rule, you'll want to validate all possible
user input.  That includes checking whether or not particular input
has been defined, whether or not it is valid for it's intended use and
whether or not it's malicious.

Applying that guideline to your situation, I would check to see if:

* the input is set
* the input is numeric

If either or those are not true, I would default the value to 1 since
division is being used. e.g.,

$iVar = 1;
if(( isset( $_REQUEST['MY_NUMBER'] )  ( is_numeric(
$_REQUEST[MY_NUMBER']))) {
  $iVar = $_REQUEST['MY_NUMBER'];
}

$iCalculatedValue = $x / $iVar;

thnx,
Christoph

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Re: [PHP] Warning: Division by zero

[Gary]

Thanks for your response.

The error I am getting is when I am defining a variable.

(line 15) $percent_difference=($assess_difference)/($assess_value);

Does this make a difference?

Thanks again for all your help.

Gary


Christoph Boget christoph.bo...@gmail.com wrote in message 
news:540509760904300600i7af94667w6bad30ed068d1...@mail.gmail.com...
 I have a script that is a result of data entered in a form
 On the script (when I test without data entry), I am getting a warning 
 that
 Warning: Division by zero in .inc.php on line 15.
 The warning is correct, however the viewer cannot access the second 
 script
 without entering the data that would cancel the warning.
 Is this something I should worry about? or would it be better to right in 
 an
 isset?

 Well, just as a general rule, you'll want to validate all possible
 user input.  That includes checking whether or not particular input
 has been defined, whether or not it is valid for it's intended use and
 whether or not it's malicious.

 Applying that guideline to your situation, I would check to see if:

 * the input is set
 * the input is numeric

 If either or those are not true, I would default the value to 1 since
 division is being used. e.g.,

 $iVar = 1;
 if(( isset( $_REQUEST['MY_NUMBER'] )  ( is_numeric(
 $_REQUEST[MY_NUMBER']))) {
  $iVar = $_REQUEST['MY_NUMBER'];
 }

 $iCalculatedValue = $x / $iVar;

 thnx,
 Christoph 



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Re: [PHP] Warning: Division by zero

[Christoph Boget]

 The error I am getting is when I am defining a variable.
 (line 15) $percent_difference=($assess_difference)/($assess_value);
 Does this make a difference?

No, it doesn't make a difference.  The simple fact is that
$assess_value is either undefined or has been set to 0 at some point.
For it's use in the above equation, neither case is valid.
Consequently, you really should be doing some validation at some point
prior to that line.

thnx,
Christoph

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