Please feel free to ask me any questions. Thanks everyone for the support.

Have you faced difficult questions in your interview?

Are you planning for certification exams and you have questions unanswered?

do you want to correct your reasoning?

Then add questions to this post and you can add as many questions as you want. Every week I will answer or compile the answer for the questions. So lets make the question bank a bigger one.

http://groups.google.com/group/phpbook/

My hats off to all the contributors and well wishers of this project. Keep up the good works.

What if we can use the third variable:

$a = 100;

$b = 200;

now we need to swap the values so that $a becomes 2oo and $b becomes 1oo.

the basic technique is to introduce a third variable $tmp

$tmp = $a;

$a = $b;

$b = $tmp;

isn’t it straight forward. introducing a third variable it is so easy. but what will be our approach if there is no third variable? is it possible?

The answer is a big YES. There are several ways and they fall in two types of solution.

1. Arithmetic operation

2. Bitwise operation.

Arithmetic Operation:

we can use addition-deduction and multiply-division method to solve the problem.

let’s see how addition – deduction method works.

<?php

$x = 10;

$y = 20;
$x = $x+$y;
$y = $x – $y;
$x = $x – $y;
?>

it is also very simple, isn’t it. first we are adding the two numbers and keeping the result in one of the variable. in the above example its $x and it contains $x+$y. in the second operation, we are deducting $y from $x and assigning it to $y. now lets break the equation logically

$y = $x – $y => $x + $y – $y => $x  // [ since $x = $x+$y ]

cool, we swapped one of the variable. and following the same operation we are swapping the second one in the third line. so that’s it. It is so easy but just requires some logical thinking. do not try to memorize it rather than understand the simple logic here.

now the multiply-division method:

<?php

$x = 10;

$y = 20;
$x = $x*$y;
$y = $x / $y;
$x = $x / $y;
?>

it is same as the addition-deduction method and logic is similar.

now do we see any problem in the above logic? that is the question i ask if someone can answer the question correctly and show me the above solution.

the answer for that is very simple, it is the number overflow as we always have upper limit for integers. so when we add or multiply two big numbers then the result can cause overflow and might not show desired results.

so what can be a good solution with keeping the overflow fact in mind? the answer is bitwise operation

Bitwise operation:

in order to swap two values we can use the XOR bitwise operator.

Note: A bitwise exclusive or takes two bit patterns of equal length and performs the logical XOR operation on each pair of corresponding bits. The result in each position is 1 if the two bits are different, and 0 if they are the same

the algorithm is

x = x XOR y

y = x XOR y

x = x XOR y

if we write them in computer language using caret (^) then it will look like

x = x ^ y

y = x ^ y

x = x ^ y

in shorter version:

x ^= y

y ^= x

x ^= y

in one line

x ^= y ^= x ^= y

so here is the command in php:

$x ^= $y ^= $x ^= $y

now how it works:

so now we know how to swap two values without using a third variable. ask me any questions you have

But that is not gonna solve your problem. when you are running CLI or shell_exec in *nix environment, php uses a different php.ini file located inside CLI folder. until you edit that the problem wont be solved. So if you are constantly getting errors after altering your php.ini file used by your web server then you should try your CLIs’ php.ini file for any issues regarding cron/CLI.

php /var/www/path/to/your/script

but if we give CodeIgniter Controller path here it will not work since CodeIgniter will fail to initialize its core classes. A work around of this is running the script using CURL

curl http://yourwebsite/controllername

the problem with the above command is that it takes too much CPU resources .

Today my collegue Hasan showed me a nice way of doing it, just write the following codes in a php file in your root folder. here is the way to go

<?
$_GET["/external/do_cron"] = null;
require “index.php”;
?>

note: here “external” is the controller name and “do_cron” is the function name that you want to execute.

now save this file to any name you want (eg. mycron.php) and run the script using

php /var/www/path/to/script

[here it is php /var/www/mywebsite/mycron.php]

if the above code does not work, you can try the following one. (thanks to sucio)

$_SERVER["REQUEST_URI"] =”external/do_cron”;
require “index.php”;

A very special thanks to Ryan Lane & Jon

Details of the extension is given below:

Screenshot:

Requirements: Mediawiki 1.9.0  and above [ I have not tested with earlier versions. ]

Steps:

1. Download the wikigallery files from here.
2. unzip it to your extensions directory
3. download wikigallery extension file from here
4. unzip it and drop it into your extensions directory
5. make sure $wgUseImageResize is enabled in your LocalSettings.php file
6. add the following lines to your LocalSettings.php file and save

include(“extensions/WikiGallery.php”);
$wgWikiGalleryExtensionPath = “/mediawiki/extensions/wikigallery”;
$wgWikiGalleryDelimiter = “\n”;

Now the extension is ready and we can use it to our wiki pages. Edit a wiki page and add the following tag with image names delimited by the wikigallery delimiter as mentioned on LocalSettings.php file (in this case its \n , but it can be , # etc). For local files (uploaded in the wiki), we do not have to put anything. but for external images the http:// must be there.

<wikigallery>

http://www.google.com/intl/en_ALL/images/logo.gif

http://ecx.images-amazon.com/images/I/41ug%2BrrN4YL._AA280_.jpg

myhome.gif
</wikigallery>

Now save and check your page , you will see the gallery is there.

Note:

•     I will try to keep the code updated with smooth gallery. But can not promise that.
•     If you have any download issue, please inform me with your email address. I will send you the scripts in email.

 Prepared statement:

Prepared statements are the ability to set up a statement once, and then execute it many times with different parameters. They are designed to replace building ad hoc query strings, and do so in a more secure and efficient manner. A typical prepared statement would look something like:

SELECT * FROM table WHERE column = ?

The ? is what is a called a placeholder. When you execute the above query, you would need to supply the value for it, which would replace the ? in the query above.

benefits:

as from Harrison Fisk article on prepared statement

Prepared statements can help increase security by separating SQL logic from the data being supplied. This separation of logic and data can help prevent a very common type of vulnerability called an SQL injection attack. Normally when you are dealing with an ad hoc query, you need to be very careful when handling the data that you received from the user. This entails using functions that escape all of the necessary trouble characters, such as the single quote, double quote, and backslash characters. This is unnecessary when dealing with prepared statements. The separation of the data allows MySQL to automatically take into account these characters and they do not need to be escaped using any special function.

The increase in performance in prepared statements can come from a few different features. First is the need to only parse the query a single time. When you initially prepare the statement, MySQL will parse the statement to check the syntax and set up the query to be run. Then if you execute the query many times, it will no longer have that overhead. This pre-parsing can lead to a speed increase if you need to run the same query many times, such as when doing many INSERT statements.

following image will illustrate the fact

Stored procedure:
A stored procedure is a precompiled executable object that contains one or more SQL statements. Hence you can replace your complex SQL statements with a single stored procedure. Since, stored procedures are precompiled objects they execute faster at the database server. For the consecutive run it will run from the compiled stage and hence boost performance.

Note: You have to choose the when to use to use what. certainly not every query should be transformed to prepared statement  or stored procedures. 

1. bangla spell checker

2. bangla wysiwyg editor (probably tinymce)

3. bangla translation

4. bangla unicode pdf

5. bangla universal writing panel with keyboard support (from somewhereinblog write panel)

if you have some cool idea, you can share with me and also you can participate in any of the projects above if you want to.

Every 2/3 weeks a new chapter will be uploaded online with all the codes and graphics so that user can read and apply the things they will learn. I hope to upload the first chapter in the first week of April.