First Steps With PHP

This is a small tutorial that will help you start with PHP
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:



All of these work in exactly the same way but in this tutorial I will be using the first option (). 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 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:

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 that 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.
Printing Text
To output text in your PHP script is actually very simple. As with most other things in PHP, you can do it in a variety of different ways. The main one you will be using, though, is print. Print will allow you to output text, variables or a combination of the two so that they display on the screen.
The print statement is used in the following way:
print("Hello world!");
I will explain the above line:
print is the command and tells the script what to do. This is followed by the information to be printed, which is contained in the brackets. Because you are outputting text, the text is also enclosed instide quotation marks. Finally, as with nearly every line in a PHP script, it must end in a semicolon. You would, of course, have to enclose this in your standard PHP tags, making the following code:

Which will display:
Hello world!
on the screen.
Variables
As with other programming languages, PHP allows you to define variables. In PHP there are several variable types, but the most common is called a String. It can hold text and numbers. All strings begin with a $ sign. To assign some text to a string you would use the following code:
$welcome_text = "Hello and welcome to my website.";
This is quite a simple line to understand, everything inside the quotation marks will be assigned to the string. You must remember a few rules about strings though:
Strings are case sensetive so $Welcome_Text is not the same as $welcome_text String names can contain letters, numbers and underscores but cannot begin with a number or underscore When assigning numbers to strings you do not need to include the quotes so:
$user_id = 987
would be allowed.
Outputting Variables
To display a variable on the screen uses exactly the same code as to display text but in a slightly different form. The following code would display your welcome text:

As you can see, the only major difference is that you do not need the quotation marks if you are printing a variable.
Formatting Your Text
Unfortunately, the output from your PHP programs is quite boring. Everything is just output in the browser's default font. It is very easy, though, to format your text using HTML. This is because, as PHP is a server side language, the code is executed before the page is sent to the browser. This means that only the resulting information from the script is sent, so in the example above the browser would just be sent the text:
Hello and welcome to my website.
This means, though, that you can include standard HTML markup in your scripts and strings. The only problem with this is that many HTML tags require the " sign. You may notice that this will clash with the quotation marks used to print your text. This means that you must tell the script which quotes should be used (the ones at the beginning and end of the output) and which ones should be ignored (the ones in the HTML code).
For this example I will change the text to the Arial font in red. The normal code for this would be:

As you can see this code contains 4 quotation marks so would confuse the script. Because of this you must add a backslash before each quotation mark to make the PHP script ignore it. The code would change to:

You can now include this in your print statement:
print("Hello and welcome to my website.");
which will make the browser display:
Hello and welcome to my website.
because it has only been sent the code:
Hello and welcome to my website.
This does make it quite difficult to output HTML code into the browser but later in this tutorial I will show you another way of doing this which can make it a bit easier.
The Basics Of IF
If statements are used to compare two values and carry out different actions based on the results of the test. If statements take the form IF, THEN, ELSE. Basically the IF part checks for a condition. If it is true, the then statement is executed. If not, the else statement is executed.
IF Strucure
The structure of an IF statement is as follows:
IF (something == something else){THEN Statement} else {ELSE Statement}
Variables
The most common use of an IF statement is to compare a variable to another piece of text, a number, or another variable. For example:
if ($username == "webmaster")
which would compare the contents of the variable to the text string. The THEN section of code will only be executed if the variable is exactly the same as the contents of the quotation marks so if the variable contained 'Webmaster' or 'WEBMASTER' it will be false.
Constructing The THEN Statment
To add to your script, you can now add a THEN statement:
if ($username == "webmaster") {echo "Please enter your password below";}
This will only display this text if the username is webmaster. If not, nothing will be displayed. You can actually leave an IF statement like this, as there is no actual requirement to have an ELSE part. This is especially useful if you are using multiple IF statements.
Constructing The ELSE Statement
Adding The ELSE statement is as easy as the THEN statement. Just add some extra code:
if ($username == "webmaster") {echo "Please enter your password below";} else {echo "We are sorry but you are not a recognised user";}
Of course, you are not limited to just one line of code. You can add any PHP commands in between the curly brackets. You can even include other IF statments (nested statements).
Other Comparisons
There are other ways you can use your IF statement to compare values. Firstly, you can compare two different variables to see if their values match e.g.
if ($enteredpass == $password)
You can also use the standard comparision symbols to check to see if one variable is greater than or less than another:
if ($age < "13")
Or :
if ($date > $finished)
You can also check for multiple tests in one IF statement. For instance, if you have a form and you want to check if any of the fields were left blank you could use:
if ($name == "" $email == "" $password == "") {echo "Please fill in all the fields";}