if condition holds true only for 0 when comparing it with string variable

Question

The output of the code below is "fail" but if we pass 1 to $b as $b=1 then it will give the output as "pass". Can anybody tell me why this if condition holds true only for 0?

<?php 
      $a="abcd"; 
      $b=0; 
      if($a == $b)
      {
         echo "fail";
      } 
      else
      { 
         echo "pass";
      }
?>

Read all about [loose typing](http://www.php.net/manual/en/types.comparisons.php) in comparisons — Mark Baker, Sep 11 '13 at 13:14
[Read the PHP documentation on type comparisons](http://php.net/manual/en/types.comparisons.php) non-numeric strings will cast to integer zero when loosely compared. — Michael Berkowski, Sep 11 '13 at 13:16
I like the fact that `$a = "123";` would "pass" because it evalutes to 123 and 123 != 0. PHP definitly favors integers. — Christoph Diegelmann, Sep 11 '13 at 13:20
@JimL `$a = "123";` <- do you often use semicolons in your ifs ?! — Christoph Diegelmann, Sep 11 '13 at 13:59

score 1 · Answer 1 · answered Sep 11 '13 at 13:16

1

That is because of PHP type juggling with == operator. The full table is given here.

answered Sep 11 '13 at 13:16

Alma Do

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score 1 · Answer 2 · answered Sep 11 '13 at 13:17

1

because you are comparing 2 variables of a different type, one of the 2 will be converted. In this case the string will be converted to an integer, which will be 0 for strings that do not start with a numeric value.

so "abc" == 0 in PHP, to add a type check use "abc" === 0

answered Sep 11 '13 at 13:17

NDM

6,731
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Nothing says "thank you" like a freshly picked upvote. Also don't forget to mark an answer as accepted when your question is resolved. – NDM Sep 11 '13 at 13:27
where would I find that option?? – Jamie Sep 11 '13 at 13:41
It says vote up requires 15 reputation. Not working for me :( – Jamie Sep 11 '13 at 13:51
there you go, upvoted ur question. marking an answer as correct should not require any rep i think. – NDM Sep 11 '13 at 13:54

George Brighton · Answer 3 · 2013-09-11T13:24:07.660

0

You're a victim of type juggling. Try using the identical comparison operator, ===, which also checks to make sure the types of variables are the same:

var_dump('abcd' === 0); // bool(false)

edited Sep 11 '13 at 13:24

answered Sep 11 '13 at 13:17

George Brighton

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Non-empty strings don't evaluate to false. – Michael Berkowski Sep 11 '13 at 13:18
Read the documentation: http://php.net/manual/en/language.operators.comparison.php – ComFreek Sep 11 '13 at 13:18
Apologies; edited my answer. – George Brighton Sep 11 '13 at 13:24

score 0 · Answer 4 · answered Sep 11 '13 at 13:21

From the PHP Manual:

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.

if($a==$b) { 
    echo "fail";
} 
else { 
    echo "pass";
}

This will output fail.

But, if you use the identical comparison operator ===, the type conversion does not take place:

if($a===$b) { 
    echo "fail";
} 
else { 
    echo "pass";
}

This will output pass.

For more details, refer to the type juggling documentation in the PHP manual.

if condition holds true only for 0 when comparing it with string variable

4 Answers4