Simple because 'ap' is NOT a key in the first case. See yourself with var_dump($pole); how the array looks like.

first case:

array(3) { [1]=> string(2) "ap" [2]=> string(2) "aa" [3]=> string(2) "dd" } 


second case:

array(3) { ["ap"]=> int(1) ["aa"]=> int(2) ["dd"]=> int(3) } 

Why is this different? Shouldn't this be the same?

as Array() definition says: 

Syntax "index => values", separated by commas, define index and values. index may be of type string or numeric. When index is omitted, a integer index is automatically generated, starting at 0. If index is an integer, next generated index will be the biggest integer index + 1. Note that when two identical index are defined, the last overwrite the first.

So I have used in first case the Example 3. 1-based index with array():

$firstquarter  = array(1 => 'January', 'February', 'March');

I thing, that the second case definition is wrong and should return error, but as I see, the function array_key_exists works with this... I'm I mad or what???

for mfischer@php.net: Can you explain me your words:

Simple because 'ap' is NOT a key in the first case.

?????

Just don't know, what you mean...

$pole = array(1 => "ap", "aa", "dd");
              |
              |
             Key

$pole = array("ap" => 1, "aa" => 2, "dd" => 3);
               |          |          |
               |          |          |
              Key        Key        Key

This is what he means, ap is NOT a KEY in the first array it is a VALUE.

The function you want is in_array() - http://www.php.net/manual/en/function.in-array.php

-Chris

Got it, thanks a lot. One hint - maybe someone should add to manual, what is key and what is it not....