OOP/Scope

LiseA

Hejsa!

I have a scope problem. My program should say, first "list empty", then "list not empty" - but says "list empty" twice. Help! Where should I say global - or what? I've tried to copy the php/oop example, but I seem to need something more.

[lisea@asterix llist]$ cat IntNode.obj
<?php
// a node in an integer singly linked list class

class IntNode {
var $info; // integer
var $next; // IntNode
function IntNode($i,$n) {
$this->info = $i;
$this->next = $n;
}
}

?>
[lisea@asterix llist]$

[lisea@asterix llist]$ cat IntSLList.obj
<?php
include "IntNode.obj";

    // singly linked list class to store integers

    class IntSSList {
            var $head; // IntNode
            var $tail; // IntNode
            function IntSLList() {
                    $head = null;
                    $tail = null;
            }
            function isEmpty() {
                    return ($head == null);
            }
            function addToHead($el) {
                    $head = new IntNode($el,$head);
                    if ($tail == null) {
                            $tail = $head;
                    }
            }
            function printAll() {
                    $tmp = $head;
                    while ($tmp != null) {
                            print $tmp->info;
                            $tmp = $tmp->next;
                    }
            }
    }

?>
[lisea@asterix llist]$

[lisea@asterix llist]$ cat test.php
<?php
// include "IntNode.obj";
include "IntSLList.obj";

    $test1 = new IntNode(2,null);
    $test2 = new IntNode(3,$test1);
    $test3 = new IntSSList();
    if ($test3->isEmpty()) {
            print "list empty<br />";
    } else {
            print "list not empty<br />";
    }
    $test3->addToHead(4);
    if ($test3->isEmpty()) {
            print "list empty<br />";
    } else {
            print "list not empty<br />";
    }
    $test3->printAll();

?>
<html><head><title>Hej verden</title></head>
<body>
Hej verden
</body>
</html>

[lisea@asterix llist]$

Thanks in advance for any help I can get!

Lise

archangel_617b

Please be sure to use [ code ] or (preferrably) [ php ] tags when posting code 🙂

Definately a scoping problem. Don't use global though, global baaaad. I get nailed with this problem often too: no variable declarations in PHP since variables are created on the fly. Therefore any variable you use in with a method is a local variable. Always use $this-> like in your IntSSList::isEmpty() you need to say

return $this->head == null;

I see this is a common fault in your code, so once you clean those up, you will get a lot more consistent results.

Hope this solves your problem. Just harass and prod if not 😉

LiseA

Hejsa!

Not quite sure where/how I should use [ code ]?

Anyway. Thanks for the help. Solved the problem. And then I ventured into making a new method....

IntNode.obj

<?php
// a node in an integer singly linked list class

class IntNode {
var $info; // integer
var $next; // IntNode
function IntNode($i,$n) {
$this->info = $i;
$this->next = $n;
}
}

IntSLList.obj

<?php
// singly linked list class to store integers

    class IntSSList {
            var $head; // IntNode
            var $tail; // IntNode
            function IntSLList() {
                    $this->head = null;
                    $this->tail = null;
            }
            function isEmpty() {
                    return ($this->head == null);
            }
            function addToHead($el) {
                    $this->head = new IntNode($el,$this->head);
                    if ($this->tail == null) {
                            $this->tail = $this->head;
                    }
            }
            function addToTail($el) {
                    if (!$this->isEmpty()) {
                            $this->tail->next = new IntNode($el,null);
                            $this->tail = $this->tail->next;
                    } else {
                            $this->tail = new IntNode($el,null);
                            $this->head = $this->tail;
                    }
            }
            function printAll() {
                    $tmp = $this->head;
                    while ($tmp != null) {
                            print $tmp->info;
                            $tmp = $tmp->next;
                    }
                    print "<br>\n";
            }
    }

test.php

<?php
include "IntNode.obj";
include "IntSLList.obj";

    $test3 = new IntSSList();
    $test3->addToTail(8);
    $test3->addToTail(9);
    $test3->printAll();

?>
<html><head><title>Hej verden</title></head>
<body>
Hej verden
</body>
</html>

Result in browser:

8
Hej verden

I suspect there's still a scope problem - that I can't influence the third step:

$this->tail->next = new IntNode($el,null);

But not sure.

Damn!

archangel_617b

Just wrap any PHP code you submit in the tags. Place [ PHP ] and [ /PHP ] (remove the spaces) around your provided code. Using the PHP tag meens your code will look something like this:

		function setUrl($str)
		{
			// strip tags, egads
			$str = strip_tags($str);

		// we need to be sure all components of the URL are present
		if (preg_match($pattern1, $str))
			$this->url = $str;		// url seems complete
		elseif (preg_match($pattern2, $str))
			$this->url = 'http://'.$_SERVER['HTTP_HOST'].$str;	
		else
			return 'Could not determine URL from ['.$str.']';
	}

See? Much butter.