PHP Tutorial

 

Introduction

Up until recently, scripting on the internet was something which very few people even attempted, let alone mastered. Recently though, more and more people have been building their own websites and scripting languages have become more important. Because of this, scripting languages are becomming easier to learn and PHP is one of the easiest and most powerful yet.

What Is PHP?

PHP stands for Hypertext Preprocessor and is a server-side language. This means that the script is run on your web server, not on the user's browser, so you do not need to worry about compatibility issues. PHP is relatively new (compared to languages such as Perl (CGI) and Java) but is quickly becomming one of the most popular scripting languages on the internet.

Why PHP?

You may be wondering why you should choose PHP over other languages such as Perl or even why you should learn a scripting language at all. I will deal with learning scripting languages first. Learning a scripting language, or even understanding one, can open up huge new possibilities for your website. Although you can download pre-made scripts from sites like Hotscripts, these will often contain advertising for the author or will not do exactly what you want. With an understanding of a scripting language you can easily edit these scripts to do what you want, or even create your own scripts.

Using scripts on your website allows you to add many new 'interactive' features like feedback forms, guestbooks, message boards, counters and even more advanced features like portal systems, content management, advertising managers etc. With these sort of things on your website you will find that it gives a more professional image. As well as this, anyone wanting to work in the site development industry will find that it is much easier to get a job if they know a scripting language.

What Do I Need?

As mentioned earlier, PHP is a server-side scripting language. This means that, although your users will not need to install new software, you web host will need to have PHP set up on their server. It should be listed as part of your package but if you don't know if it is installed you can find out using the first script in this tutorial. If you server does not support PHP you can ask your web host to install it for you as it is free to download and install. If you need a low cost web host which supports PHP I would recommmend HostRocket.

Writing PHP

Writing PHP on your computer is actually very simple. You don't need any specail software, except for a text editor (like Notepad in Windows). Run this and you are ready to write your first PHP script.

Declaring PHP

PHP scripts are always enclosed in between two PHP tags. This tells your server to parse the information between them as PHP. The three different forms are as follows:

<?
PHP Code In Here
?>

<?php
PHP Code In Here
php?>

<script language="php">
PHP Code In Here
</script>

All of these work in exactly the same way but in this tutorial I will be using the first option (<? and ?>). There is no particular reason for this, though, and you can use either of the options. You must remember, though, to start and end your code with the same tag (you can't start with <? and end with </script> for example).

Your First Script

The first PHP script you will be writing is very basic. All it will do is print out all the information about PHP on your server. Type the following code into your text editor:

<?
phpinfo();
?>

As you can see this actually just one line of code. It is a standard PHP function called phpinfo which will tell the server to print out a standard table of information giving you information on the setup of the server.

One other thing you should notice in this example is th
at the line ends in a semicolon. This is very important. As with many other scripting and programming languages nearly all lines are ended with a semicolon and if you miss it out you will get an error.

Finishing and Testing Your Script

Now you have finished your script save it as phpinfo.php and upload it to your server in the normal way. Now, using your browser, go the the URL of the script. If it has worked (and if PHP is installed on your server) you should get a huge page full of the information about PHP on your server.

If your script doesn't work and a blank page displays, you have either mistyped your code or your server does not support this function (although I have not yet found a server that does not). If, instead of a page being displayed, you are prompted to download the file, PHP is not installed on your server and you should either serach for a new web host or ask your current host to install PHP.

It is a good idea to keep this script for future reference.

Part 2

In this part I have introduced you to the basics of writing and running PHP. By this time you should now know if your host supports PHP and should have a basic understanding of how PHP scripts are structured. In part 2 I will show you how to print out information to the browser.

PHP 5.x is standard on iPage™ hosting (see tutorials for website setup help), which supports the most popular PHP scripts and content management systems.

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A PHP Times Table Programme

In the previous part, you saw what a For Loop was. In this section, we'll write a times table programme to illustrate how for loops work.
There's a script called timesTable.php amongst the files you downloaded (in the scripts folder). When loaded into the browser, it looks like this:
There's a script called timesTable.php amongst the files you downloaded (in the scripts folder.). When loaded into the browser, it looks like this:

What we're going to do is to get the values from the textboxes and create a Times Table proramme. When the button is clicked, the output will be something like this:

In other words, when the button is clicked we'll print the Times Table to the page. You can have a different Times Table, depending on what values you enter in the textboxes. To make a start with the coding, move on to the next part.

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Some Practise with PHP If Statements

We can use an if statement to display our image, from the previous section. If the user selected "church", then display the church image. If the user selected "kitten", then display another image (the kitten image, which is also in your images folder). Here's some code:

<?PHP

$kitten_image = 1;
$church_image = 0;

if ($kitten_image == 1) {

print ("<IMG SRC =images/kitten.jpg>");

}

?>

Type that out, and save it as testImages.php. (Notice how there's no HTML!)
When you run the script, the kitten image should display. Let's look at the code and see what's happening.
The first two lines just set up some variables:

$kitten_image = 1;
$church_image = 0;

A value of 1 has been assigned to the variable called $kitten_image. A value of 0 has been assigned to the variable called $church_image. Then we have our if statement. Here it is without the print statement:

if ($kitten_image == 1) {

}

Notice how there's no semi-colon at the end of the first line - you don't need one. After the word "if" we have a round bracket. Then comes our variable name: $kitten_image. We want to test what's inside of this variable. Specifically, we want to test if it has a value of 1. So we need the double equals sign (==). The double equals sign doesn’t really mean “equals”. It means “has a value of”.
What we want to say is:

"If the variable called $kitten_image has a value of 1 then execute some code."

To complete the first line of the if statement we have another round bracket, and a left curly bracket. Miss any of these out, and you'll probably get the dreaded parse error!
The code we want to execute, though, is the print statement, so that our kitten image will display. This goes inside of the if statement:

if ($kitten_image == 1) {

print ("<IMG SRC =images/kitten.jpg>");

}

You need the semi-colon at the end of the print statement.
But if your if statement only runs to one line, you can just do this:

if ($kitten_image == 1) { print ("<IMG SRC = images/kitten.jpg>"); }

In other words, keep everything on one line. PHP doesn't care about your spaces, so it's perfectly acceptable code. Not very readable, but acceptable!
To make use of the church image, here's some new code to try:

<?PHP

$kitten_image = 0;
$church_image = 1;

if ($kitten_image == 1) {

print ("<IMG SRC =images/kitten.jpg>");

}

if ($church_image == 1) {

print ("<IMG SRC =images/church.jpg>");

}

?>

Notice that the $kitten_image variable now has a value of 0 and that $church_image is 1. The new if statement is just the same as the first. When you run the script, however, the church image will display. That's because of this line:

if ($kitten_image == 1) {

That says, "If the variable called $kitten_image has a value of 1 ... ". PHP doesn't bother reading the rest of the if statement, because $kitten_image has a value of 0. It will jump down to our second if statement and test that:

if ($church_image == 1) {

Since the variable called $church_image does indeed have a value of 1, then the code inside of the if statement gets executed. That code prints out the HTML for the church image:

print ("<IMG SRC =images/church.jpg>");

In the next section, we'll take a look at if ... else statements.

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What you need to get started with PHP

Before you can write and test your PHP scripts, there's one thing you'll need - a server! Fortunately, you don't need to go out and buy one. In fact, you won't be spending any extra money. That's why PHP is so popular! But because PHP is a server-sided scripting language, you either have to get some web space with a hosting company that supports PHP, or make your computer pretend that it has a server installed. This is because PHP is not run on your PC - it's executed on the server. The results are then sent back to the client PC (your computer).
Don't worry if this all sounds a little daunting - we've come across an easier way to get you up and running. We're going to be using some software called Wampserver. This allows you to test your PHP scripts on your own computer. It installs everything you need, if you have a Windows PC. We'll explain how to get it installed in a moment, and where to get it from. But just a word for non-windows users.

Apple Users

If you have OS X, then try these sites to get up and running with PHP:

http://www.onlamp.com/pub/a/mac/2001/12/07/apache.html

http://www.entropy.ch/software/macosx/php/

What you're doing here is getting the apache server up and running, so that you can run PHP scripts offline. Pay particular attention to where files are stored, and to the "localhost" address.

Linux Users

There are quite a few sites out there to help Linux users get up and running with the Apache server and PHP. Here are three sites that are worth checking out:

http://en.wikipedia.org/wiki/LAMP_(software_bundle)

http://www.php-mysql-tutorial.com/wikis/php-tutorial/installing-php-and-mysql.aspx

http://www.phpfreaks.com/tutorials/12/0.php

If you know any better ones, we'd be interested in hearing from you!

Windows Users

OK, back to Wampserver and Windows. First, you need to download the software. You can get it from here (this site is nothing to do with ours, by the way):

Download Wampserver

Be sure to click the link for Presentation, as well as the link for Downloads. The Presentation page shows you how to install the file.

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What is PHP?

PHP is probably the most popular scripting language on the web. It is used to enhance web pages. With PHP, you can do things like create username and password login pages, check details from a form, create forums, picture galleries, surveys, and a whole lot more. If you've come across a web page that ends in PHP, then the author has written some programming code to liven up the plain, old HTML.
PHP is known as a server-sided language. That's because the PHP doesn't get executed on your computer, but on the computer you requested the page from. The results are then handed over to you, and displayed in your browser. Other scripting languages you may have heard of are ASP, Python and Perl. (You don't need to know any of these to make a start on PHP. In fact, these tutorials assume that you have no programming experience at all.)
The most popular explanation of just what PHP stands for is "Hypertext Pre-processor". But that would make it HPP, surely? An alternative explanation is that the initials come from the earliest version of the program, which was called Personal Home Page Tools. At least you get the letters "PHP" in the right order!
But PHP is so popular that if you're looking for a career in the web design/web scripting industry then you just have to know it! In these tutorials, we'll get you up and running. And, hopefully, it will be a lot easier than you think.

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