php 5 class includes crashing server.

[distorto]

I have sort of isolated this problem to my file that calls all of my classes using require_once. I can make the system crash by including an extra class in the list, so I'm assuming there's some problem there. I know this sounds vague, but my real question is about a couple general topics when working with classes in php5.

class definitions include a list of properties - or variables. In many code examples, I have seen classes in which there are variables used throughout the code that weren't declared at the top. What's the deal here? Is it required?

here's an example of this

class A {

public $var1;
public $var2;

function __construct(){
$this->var1 = '';
$this->var2 = '';
}

public function func1($pass){
$var3 = $pass * 2;
echo $var3;
}
}

was $var3 supposed to be declared at the top?

what if it was changed to:

$this->var3 = $pass * 2;
echo $this->var3;

would that make a difference? is that wrong?

also, the problem I'm encountering relates to a pagination class (Pagination.class.php) that I'm trying to attach to everything that requires pagination. I made the pagination class and made two other classes: class A and class B

i wrote the top of these like so:

<?php
include 'Pagination.class.php';

class A extends Pagination {}
?>

and

<?php
include 'Pagination.class.php';

class B extends Pagination {}
?>

Is there something fundamentally wrong with this? I have been searching like crazy for answers and have found a ton of resources, but no answers to these questions.

[PHP_Chimp]

public function func1($pass){
$var3 = $pass * 2;
echo $var3;
}
}

$var3 doesnt have to be declared at the top of your code. If you declare it then it will be available thought the whole of your code.
Although this is not correct it may help to think of the variables that you declare at the top as global variables, or maybe that $this-> is the same as the word global. So you can use $this->something to access them at any point in your script. If you wanted to use $var3 in another place then you would need to use the global $var3 to put it there.

I have had issues getting constructors to load from parent classes, so if you code is based on the constructor from a parent class then I would check that this is actually getting loaded into the child class.

[cameraman]

By make the system crash do you mean that the script stops executing with an error or the computer executing the server software locks up/reboots or that the server software stops serving until it is manually restarted?

If you're including both your class A and class B scripts in another script, try replacing
include 'Pagination.class.php';
in each of them with
include_once [php.net] 'Pagination.class.php';

$var3 is just a local variable in the function in your example. $var1 and $var2 are, as you mentioned, properties or member variables of the class. $var3 doesn't exist outside func1() whereas $var1 and $var2 exist as long as a class object exists. They aren't global per se, they are local to a particular object:
$obj1 = new A;
$obj1 -> var1 = 7;
$obj1 -> var2 = 8;

$obj2 = new A;
$obj2 -> var1 = 3;
$obj2 -> var2 = 4;

$obj1 and $obj2 have different values for their member variables.