Variables

Variables are containers, they contain data. PHP is a loosely typed language, and thus the variable can contain any type of data, PHP will change the type of the variable implicitly, depending on the operation being performed on it. This is in strong contrast with strongly typed languages, such as Java, or C++, where a variable can only hold one data type troughout its whole life.
[ad]In PHP, variables are identified by the dollar sign: $, followed by the name you wish to give to your variable. These names can contain bot upper- and lowercase letters, numbers, and the underscore character. Other characters are not allowed in variablenames. The name can start with any letter, or an underscore, but never with a number. So, $varname, $Varname and $_varname are all correct, $1varname is not correct.

Variable variables
PHP offers the extremely powerful possibility to create what is called a variable variable. This is a variable whose name is contained in another variable. An example:

$varname = ‘Tom’;
/* Tom is the name of the variable */
$$varname = ‘Tim’;
/* Tim is the value you assign to the variable named Tom. You do this through the variable $varname, which holds the the variablename Tom */
echo $Tom;
/* This will display ‘Tim’ */

The same works with numbers! This means you can circumvent the variable naming restrictions mentioned above. You can also do this by defining the name between braces: ${123};
And, even better, there is also something similar to variable variables, but with functions. This means you can put a function name inside a variable, and execute the function by calling the variable.

function anyFunction(){
echo ‘icantinternet.org rules!’;
}

$anyVar = ‘anyFunction’;
$anyVar();  //This will call and execute the function anyFunction, and echo the truth!

I suppose it holds no surprise that all this is extremely powerful, and must be used with extreme caution to avoid programming mistakes, and possibly hacking risks.

Does a variable exist?
This is a question that is not always easy to answer, due to the way PHP handles its varuables. This can lead to annoying warnings when running a scripts, up to security and functionality issues. Luckily, PHP also has a special construct to check if a variable exists and has a value set (this means, other than NULL): isset()
echo isset ($astupidvariable);

Calling isset() will return a true to you if a variable exists and has a value (other than NULL), and will return false to you when your variable doesn’t exist yet, or doesn’t have a value yet.

Constants

On the other side of the ring are the constants, which are, conversely to variables, meant for constant values (I know, it was a blinding flash of the obvious). The visibility of a constant is throughout the whole script, but, unlike variables, they can only hold scalar data, no compound data.
Constants follow the same naming conventions as variables do, so upper- and lowercase letters, numbers, and underscore, but not starting with numbers. Also, constant names do not have a leading dollar sign $. Best practice is to define your constants in all uppercase. This will give you clearer and better understandable (and thus maintainable) code.

define (‘GREATEST_SITE’, ‘icantinternet.org’); //valid name, now, throughout the code, it is known that icantinternet.org is in the constant GREATEST_SITE
echo GREATEST_SITE; //Displays the truth again (icantinternet.org for those who didn’t get it ).

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Today’s PHP lesson is about data types. Although PHP can work with many different data types, we divide them in two different categories: scalar data and composite data.

Scalar data

Scalar data can hold only one value at a time. PHP knows four different types of scalar data:
Boolean: possible values are TRUE or FALSE
[ad]int: can be any signed (so both positive and negative values are possible) numeric integer value
float: can be any signed (so both positive and negative values are possible) floating-point value
string: can be any collection of binary data

Numeric values
Numeric values can be both of the type integer as floating point, and can be annotated in decimal, octal (identified by leading zero) or hexadecimal (identified by leading 0x), and for floating-popint numbers, they can be annotated in decimal and exponential (2E7, 2.3E5).
A very important thing to note when working with numbers i s that the precision and the range of your data types depends on the machine you are working on. For instance, & 64-bit system will have a wider range than a 32-bit system. Also, PHP doesn’t track overflows. So stuffing your variable with too much data will NOT throw an error, but will result in a truncated value.
Another thing to keep in mind is that floats are not always storing their value the way you would think. For example, if you execute the statement

integervar (int) (0.2 + 0.4) * 10);
print integervar;

The printed result will not be 6 as you would expect, but it will be 5. This is because the result of 0.2 and 0.4 is not stored as 0.6 in the float, but as 0.59999999, and times ten, this gives 5.999999
When this float is conversed to an int, it simply truncates everyting behind the fraction, resulting in 5.
These things are not necessarily a disaster, but are limitations you should be aware of when doing calculations in your PHP code.

Strings
When talking about strings, most programmers immediately think of text. This is indeed the case. In some languages. Not in PHP, oh no. In PHP, a string is an ordered collection of binary data. This data can be text, but can also be an image, an office document, or a mp3-file.
Due to the extended character of strings, and all that is possible with them in PHP, we will get back on them later.

Booleans
Booleans are the easiest of all variables, as they can only hold one of two values: true or false, and are therefor mostly used in logical operations.
There are some important things to know about booleans and conversions though:
When you convert any number (no matter if it is an integer or a float) to a boolean, the boolean will always be true, except when the value of the number is zero.
When you convert a string to a boolean, the boolean will always be true, except when the string is empty (null), or contains a single digit 0 (zero). When there are multiple zeros in the string (00000), the boolean will convert to true.
When you convert a boolean to a string, integer or float, the value will be 1 if the boolean was true, and 0 if the boolean is false.

Composite Data

PHP doesn’t only support the scalar data types we discussed above, but also supports two compound or composite datatypes. The name compound or somposite comes from the fact that they are in essence containers of other data.

Arrays
Arrays contain data of other datatypes in an ordered way. Arrays can contain any of the abovementioned scalar data. We will digg deeper into arrays in a future lesson.

Objects
Objects contain both data and code. Objects are the cornerstones of Object Oriented Programming (OOP) (who would’ve thought, right?), and are also dugg into in a future lesson.

Special Data Types

Besides the two data types we mentioned above, there are also two very special data types:

NULL
Null indicates that a variable has no value. A variable can get the NULL value by getting it specifically assigned, or by not yet having been assigned any value at all.

Resource
The resource data type is used when dealing with external resources that are not part of PHP, but are used inside your code, for example a file.

Converting between data types

PHP is very easy when it comes to converting data types, as it does all the work for you, for free! However, if you really want to convert a variable to another data type yourself, you can do this by putting the name of the data type you want to convert to between parentheses, and place it in front of the expression or variable you want to convert. Check it out, it was already there in the example we used before:

integervar (int) (0.2 + 0.4) * 10);

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What is PHP?

PHP is a scripting language, primarily intended to generate dynamical websites on a webserver. PHP is designed in 1994, by a senior software engineer at IBM, Rasmus Lerdorf, and the language was clearly inspired by Perl. The letters PHP used to mean Personal Homepage (or more complete: Personal Home Page/Forms Interpreter, PHP/FI). However, during the later developments, PHP became a recursive acronym, meaning “PHP: Hypertext Preprocessor”, which better suits what the language actually does: outputting hypertext (HTML or XHTML).
Since PHP is a server side scripting language, it means that the code is not compiled, but interpreted at the time of usage (by the interpreter, most often integrated in the webserver), and that the script runs on the server side, or the webserver. This way, the output is generated on the webserver, and sent to the client (your browser) as HTML.
PHP syntax is derived from many other languages, but mainly by C and Perl. However, since PHP5 also allows for object oriented programming, there is also an influence of Java noticeable. Despite all these different influences, PHP manages to remain simple and understandable.

The Source and the Tags

Although PHP is primarily intended as a text processor, it is often used as a pure programming language. However, to facilitate its text processor role, it can be inserted in a text file as well, by using the special PHP tags. Four different tags can be used to insert and execute PHP code in a text file:

• Standard tags, these are the most commonly used tags, and are the ones you should use:
  <?php
  …
  ?>

• Short tags, used to be the standard, but might interfere with XML headers, and therefor are used more rarely:
  <?
  …
  ?>

  One advantage is that they make really short syntax possible, such as <?=$variable ?> which prints the result of the variable straight to the output.

• Script tags were introduced for HTML editors. These editors are programmed to ignore JavaScript code (which uses the same script tags), but were unable to ignore PHP code, which is fixed by these script tags:
  <script language=”PHP”>
  …
  </script>

• ASP tags, don’t ask, nobody seems to know why these were introduced…
  <%
  …
  %>

Normally, the only tags you should use are the standard tags. Short tags, script tags and ASP tags are all considered deprecated.

The newline horror

Very important to remember is that the PHP interpreter outputs EVERY character outside the PHP tags as-is. This means every whitespace, every newline character. This is not an issue for whitespaces, but can be for newline characters, as they are used as a seperator between the header portion of the http response, and the actual data. This means that a newline character that is sent to the output before the headers are finished, will cause your script to fail. To help you prevent this problem, the PHP interpreter automatically strip the first newline character after the PHP closing tag (?>).

The body of a PHP script

The body of a PHP script consists of statements, which can be function calls, variable assignments, data output etcetera. Each statement, with only a few exceptions, needs to be terminated by a semicolon. One of the exceptions is for instance the last statement before a closing tag. However, for consistency’s sake, it is advised to always terminate your statements.

Comments are another almost vital part of any programming language. Yes, I know, they are not vital at all, but you should treat them like that. Make it a habit to write comments every function, class, method or property that you write in your code. If your code required some thinking to find how you will actually code it, it will require some thinking again later when you try to reread your code, and find out why you actually coded it that way. Comments can only make your life easier!
The different ways of inserting comments in a PHP script are these:

// a single line comment

# another single line comment

/* a multiline
comment
*/

/**
* another multiline comment
* Most often used to document API’s or functions, since they can hold large parts of structured text
* and still look… err… structured.
*/

Both single line comments (// and #) are closed by a newline character, or by the PHP closing tag.

Code blocks are a series of statements that must be executed all together, and under specific circumstances, such as a function call or a conditional statement. The statements inside code blocks are enclosed with two curly brackets ({}).

if ($whatimsaying == “yaddayadda”)
then
{
$takeanapforsometime = 5;
fall_asleep_for_how_long($takenapforsometime);
}

That’s all for today folks. More is coming up in the next lesson, which will start with Datatypes!

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ASP.NET

Microsoft ASP.NET Developer Center
http://msdn.microsoft.com/asp.net
The Microsoft-homepage for ASP.NET-developpers with documentation and community

ASP Free
www.aspfree.com
Website of independent ASP-programmers with help, trics, manuals, blogs, forum and information about ASP.NET

ASPNL
www.aspnl.com
Usefull information about ASP and .NET Framework, including ASP.NET
[ad]

JavaScript/JScript

JavaScript tutorials
javascript.internet.com
The website includes tutorials, download center, blog, community and resources

Javascript.com
www.javascript.com
This website includes community center, forums, blog and research centers

Perl

Perl-FAQ
faq.perl.org
FAQ’s about Perl: getting your answers!

Perl-community
perlmonks.org
Community about Perl with information for developpers, downloads and tips

Perl.org
www.perl.org
Perl-Community with information about Perl-developping, downloads and programmingtips

Perl-archive
www.perlarchive.com
The international Perl-archive: a learning-center with articles, examples and tutorials

PHP

PHP-community
www.php.net
Website with manuals, downloads, faq, mailinglists

PHP-Tutorial
www.w3schools.com/PHP
Learning PHP from scratch

Python

Python.org
www.python.org
Website with tutorials, downloads and documentation

Python-newsgroup
www.news:com.lang.python
Python-newsgroup.

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As said in my 2009 predictions, the iPhone, and other mobile devices, will get a larger share in the tools your visitors use to visit your websites. So I suppose you will not be surprised when I tell you that it is very important to sure that your website is ready to receive your mobile customers.

[ad]The first step in this, is to let your webpage recognize if it is being visited by an iPhone. The best way to do this is by checking on the “user agent string”. For the not-knowers: this is a string of information of itself and its system that the browser sends to the webserver. In case of an iPhone, the user agent string looks something like this, depending on the language, the firmwareversion, and the country of origin:

- Mozilla/5.0 (iPhone; U; XXXXX like Mac OS X; en) AppleWebKit/420+(KHTML, like Gecko) Version/3.0 Mobile/241 Safari/419.3

- Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+(KHTML, like Gecko) Version/3.0 Mobile/21A537a Safari/419.3

This user agent string can easily be used to detect if your webpage visitor is using an iPhone or a regular browser. The following short pieces of code return the user agent string, and show it in your webpage:

JavaScript:

<script type=”text/javascript”>

document.write(navigator.userAgent);

</script>

ASP:

<%=Request.ServerVariables(“HTTP_USER_AGENT”)%>

PHP:

<?php

eco $_SERVER['HTTP_USER_AGENT'];

?>

As you may or may not know, once you can determine the type of browser being used, it is rather simple to forward Mobile Safari to the correct, iPhone optimized index page (perhaps called iphone_index.html or something):

Javascript:

<html>

<head>

<script type=”text/javascript”>

window.onload=function(){

var agent=navigator.userAgent.toLowerCase();

var is_iphone=agent.indexOf(“ipone”) !=-1;

if(is_iphone){

window.location=”iphone_index.html”

}else{

window.location=”other_index.html”;

}

}

</script>

<body>

</body>

</html>

ASP:

<%

useragent = Request.ServerVariables(“HTTP_USER_AGENT”)

if instr(useragent, “iphone”) > 0 then

response.redirect(“iphone_index.html”)

else

response.redirect(“regular_index.html”)

end if

%>

PHP:

<?php

$useragent= $_SERVER['HTTP_USER_AGENT'];

if(strpos($useragent, ‘iphone’ > 0) {

header(“Location: iphone_index.html”);

}else{

header(“Location: regular_index.html”);

}

?>

Of course, once you have this script in one of these languages to check if it is an iPhone, it can easily be extended to check for other types of browsers, and create optimized indexpages for those too.

Happy coding!

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By default, when you add a bookmark to a page to your homescreen (by tapping bookmark->add to homescreen), your iPhone will create a button for the webapp by itself.
[ad]This is miniature version of the page you were on when you created the bookmark.

There is a way however, to make the iPhone show the icon on the homescreen that YOU, being the webdeveloper, want:

- Use an imaging program (such as The Gimp)to create an image of 57×57 pixels.

- Save the image as icon.png, and upload this image to the root folder of your website.

- Add the code below to the Head section of your webpage:

<link rel=”apple-touch-icon” href=”http://www.icantinternet.org/icon.png”>

Do you want to learn to create iphone apps with no programming experience? Check out this link!

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While Digging away through my shouts on Digg, I came across this very interesting article on noupe.com, listing 21 iPhone apps that can help you boost your productivity if you are a blogger, designer or freelancer.

[ad]As an example, there are colorpickers in the list, which will give you the colorvalue of your selection in different notations, there is the wordpress app, which will let you post new articles on your wordpress.com or selfhosted wordpress blog, there are texteditors in different flavors and shapes, and there even is a VNC interface, so you can use your iPhone to work on your Mac, Windows or even Linux machine.
You can find the article here: http://www.noupe.com/tools/top-20-iphone-apps-for-bloggers-designers-freelancers.html

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When creating a website specifically aimed at the iPhone, there are some cool things you can do to improve your visitor’s iPhone web-experience.
[ad]
Show a movie
It’s very easy to add a movie to a webpage. But, if you put an image in there instead, and link to the movie, the movie will open in the iPhone’s videoplayer instead of Safari.

<embed src=”mymovie.jpg” href=”mymovie.mov” widt=”380″ height=”290″>

Link to a telephonenumber
To add a link to a telephonenumber on a webpage, that will automatically be dialled when clicked, use this code:

<a href=”tel:01234567890″>Tel: 01234567890</a>

Hide the statusbar
Safari gives you the opportunity to automatically hide the statusbar when your webpage is being loaded:

<script type=”text/javascript”>
window.onload=function(){
window.scrollTo(0,1);
}
</script>

Enjoy!

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Good SEO starts with good linking tactiques. And good linking tactiques starts with internal linking.
A first way to show to your visitors, and to Google what is important to you, and how your website is built, is by using good internal linking.
Here are some internal linking tips:

Use spiderable navigation. Either use text based navigation (only text between your anchor tags), or if you use image based navigation, make sure you add well defined alt attributes attached to each image link. Best is if you use relevant keywords in your linktext or alt attributes.

Breadcrumbs (the home>>articles>>health>>articleabouthealth type of things you see on the top of some webpages) are a great internal linking tool. They can be used for both usability and anchor text differentiation.

In-content links are simply great. Not only do they tend to have a higher click through rate and perceived trust, but they also add more relevance to a link because of the textaround it. And not only your regular visitor will see it that way, Google also does!

Create a sitemap-page. A good sitemap is useful for your cherised visitors, useful for Google and other search engines and thus useful for you. Besides the sitemap-page, you should also create an XML-sitemap, which you can submit to the search engines. However, this is not about internal linking, and thus will be covered in a future post.

Link to other relevant pages on your website, preferrably important pages (with high PR, or good keyword density). Link to important pages on every (or at least most) topically relevant page of your website.

Use your links consistently, always use the same type of url to link to, for instance, if you use http://www.icantinternet.org in your links, then stick to that. Do not use other types that land on the same page, such as http://icantinternet.org, or http://www.icantinternet.org/ or http://www.icantinternet.org/index.php

Find the pages on your website to which most links come in from outside your website (you can use Google or Yahoo! for that), and create links from your other pages towards those pages, in an optimised manner.

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