Principles of PHP

Here is a very short introduction to the principles of PHP.  PHP is an acronym for “hypertext preprocessor”. PHP is a serverside language. We use PHP in order to prepare webpages, react to user input – and (on the third semester) to interact with databases.

Many Open Source CMSs use a combination of Apache, PHP and MySQL as an “engine”.

How to write PHP code

A php file is made in a manner similar to a HTML file. You create a file and give it the surname .php. So a file name sample could be:

  • myFile.php

The file can contain other forms of code and tags such as JavaScript, CSS or HTML. In the file the php code is nested between a <? and ends with a ?>.

Variables, Strings and numbers

$a = 10; // a number
$b = “Hello World”; // a string
$c = “Ho, ho, hooo!”; // yes it’s another string
$d = “Santa Claus, says: “; // xmas is near
$combinedStrings = $d . $c; // Santa Claus, says: Ho, ho, hooo!
$e = NULL; // no value set
$f = true; // or false

A variable is defined via the $ character. In the sample code above you can see several variables.

A string starts and ends with a quotation mark as ” or ‘. If you need quotation marks inside a string they should be nested like this:

<? $foo = “<img src=’image.png’  alt=’an image’ />”; ?>

You can create HTML code via PHP – and you can show an image on a web page like this:

<? echo $foo; ?>


<? print(“$foo”); ?>


Since a variable can be a number, you can use PHP for calculations, such as:

$x = 1;
$y = 19;
echo $x + $y; // should return 20

See this page for more information about PHP and calculations.






Published by

Per Thykjaer Jensen

I am a Senior Lecturer in front- and backend web programming at the Multimedia Design and Communication Programme at Business Academy Aaarhus. I speak several languages: PHP, Python, MySQL, JavaScript, Nodejs, HTML, CSS, and ... Danish. Background: MA it, interaction and multimedia - MA Literature history - BA Art History.

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