Arithmetic error involving 0

[Bob Stearns]

I get the output:

age=0;

age=0;

from the following code:

$debug .= "<br>age=$age;< br>";
if($age!="unk") $age = $age+1;
$debug .= "<br>age=$age;< br>";

What is going on?

[dspohn]

Re: Arithmetic error involving 0

why do you have semicolons after $age inside of the quotations?

remove those, and see if you still get the error.

[Chris Hope]

Re: Arithmetic error involving 0

Bob Stearns wrote:
[color=blue]
> I get the output:
>
> age=0;
>
> age=0;
>
> from the following code:
>
> $debug .= "<br>age=$age;< br>";
> if($age!="unk") $age = $age+1;
> $debug .= "<br>age=$age;< br>";
>
> What is going on?[/color]

IIRC there are some odd issues in PHP when comparing 0 with a string. If
you change it to do a strict type check with !== it solves the
immediate issue:

if($age!=="unk" ) $age = $age+1;

--
Chris Hope | www.electrictoolbox.com | www.linuxcdmall.com

[Chris Hope]

Re: Arithmetic error involving 0

dspohn wrote:
[color=blue]
> why do you have semicolons after $age inside of the quotations?
>
> remove those, and see if you still get the error.[/color]

And why do you think that would make a difference?

--
Chris Hope | www.electrictoolbox.com | www.linuxcdmall.com

[Chris Hope]

Re: Arithmetic error involving 0

Chris Hope wrote:
[color=blue]
> Bob Stearns wrote:
>[color=green]
>> I get the output:
>>
>> age=0;
>>
>> age=0;
>>
>> from the following code:
>>
>> $debug .= "<br>age=$age;< br>";
>> if($age!="unk") $age = $age+1;
>> $debug .= "<br>age=$age;< br>";
>>
>> What is going on?[/color]
>
> IIRC there are some odd issues in PHP when comparing 0 with a string.
> If you change it to do a strict type check with !== it solves the
> immediate issue:
>
> if($age!=="unk" ) $age = $age+1;[/color]

I found the reason.

From: http://www.php.net/manual/en/languag...comparison.php

"If you compare an integer with a string, the string is converted to a
number. If you compare two numerical strings, they are compared as
integers."

var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true

Unless it is at all numerical the string will be converted to 0 making a
comparison with 0 true. In your example the comparison ends up being
0 != 0 which is of course false.

--
Chris Hope | www.electrictoolbox.com | www.linuxcdmall.com

[Bob Stearns]

Re: Arithmetic error involving 0

Chris Hope wrote:[color=blue]
> Chris Hope wrote:
>
>[color=green]
>>Bob Stearns wrote:
>>
>>[color=darkred]
>>>I get the output:
>>>
>>>age=0;
>>>
>>>age=0;
>>>
>>>from the following code:
>>>
>>>$debug .= "<br>age=$age;< br>";
>>>if($age!="un k") $age = $age+1;
>>>$debug .= "<br>age=$age;< br>";
>>>
>>>What is going on?[/color]
>>
>>IIRC there are some odd issues in PHP when comparing 0 with a string.
>>If you change it to do a strict type check with !== it solves the
>>immediate issue:
>>
>>if($age!=="un k") $age = $age+1;[/color]
>
>
> I found the reason.
>
> From: http://www.php.net/manual/en/languag...comparison.php
>
> "If you compare an integer with a string, the string is converted to a
> number. If you compare two numerical strings, they are compared as
> integers."
>
> var_dump(0 == "a"); // 0 == 0 -> true
> var_dump("1" == "01"); // 1 == 1 -> true
>
> Unless it is at all numerical the string will be converted to 0 making a
> comparison with 0 true. In your example the comparison ends up being
> 0 != 0 which is of course false.
>[/color]
I saw that some time ago and forgot it. Thanks for the reminder.

[Bob Stearns]

Re: Arithmetic error involving 0

Chris Hope wrote:
[color=blue]
> Bob Stearns wrote:
>
>[color=green]
>>I get the output:
>>
>>age=0;
>>
>>age=0;
>>
>>from the following code:
>>
>>$debug .= "<br>age=$age;< br>";
>>if($age!="unk ") $age = $age+1;
>>$debug .= "<br>age=$age;< br>";
>>
>>What is going on?[/color]
>
>
> IIRC there are some odd issues in PHP when comparing 0 with a string. If
> you change it to do a strict type check with !== it solves the
> immediate issue:
>
> if($age!=="unk" ) $age = $age+1;
>[/color]
I saw that some time ago and forgot it. Thanks for the reminder.