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:
<?
print("Hello world!");
?>
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:
<?
$welcome_text = "Hello and welcome to my website.";
print($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 chang
e 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";
}
The WHILE Loop
The WHILE loop is one of the most useful commands in PHP. It is also quite easy to set up and use. A WHILE loop will, as the name suggests, execute a piece of code until a certain condition is met.
Repeating A Set Number Of Times
If you have a piece of code which you want to repeat several times without retyping it, you can use a while loop. For instance if you wanted to print out the words "Hello World" 5 times you could use the following code:
$times = 5;
$x = 0;
while ($x < $times) {
echo "Hello World";
++$x;
}
I will now explain this code. The first two lines are just setting the variables. The $times variable holds the number of times you want to repeat the code. The $x variable is the one which will count the number of times the code has been executed. After these is the WHILE line. This tells the computer to repeat the code while $i is less than $times (or to repeat it until $i is equal to $times). This is followed by the code to be executed which is enclosed in { }.
After the echo line which prints out the text, there is another very important line:
++$x;
What this does is exactly the same as writing:
$x = $x + 1;
It adds one to the value of $x. This code is then repeated (as $x now equals 1). It continues being repeated until $x equals 5 (the value of times) when the computer will then move on to the next part of the code.
Using $x
The variable counting the number of repeats ($x in the above example) can be used for much more than just counting. For example if you wanted to create a web page with all the numbers from 1 to 1000 on it, you could either type out every single one or you could use the following code:
$number = 1000;
$current = 0;
while ($current < $number) {
++$current;
echo "$current";
}
There are a few things to notice about this code. Firstly, you will notice that I have placed the ++$current; before the echo statement. This is because, if I didn't do this it would start printing numbers from 0, which is not what we want. The ++$current; line can be placed anywhere in your WHILE loop, it does not matter. It can, of course, add, subtract, multiply, divide or do anthing else to the number as well.
The other reason for this is that, if the ++$current; line was after the echo line, the loop would also stop when the number showed 999 because it would check $current which would equal 1000 (set in the last loop) and would stop, even though 1000 had not yet been printed.
Arrays
Arrays are common to many programing languages. They are special variables which can hold more than one value, each stored in its own numbered 'space' in the array. Arrays are extremely useful, especially when using WHILE loops.
Setting Up An Array
Setting up an array is slightly different to setting up a normal variable. In this example I will set up an array with 5 names in it:
$names[0] = 'John';
$names[1] = 'Paul';
$names[2] = 'Steven';
$names[3] = 'George';
$names[4] = 'David';
As you can see, the parts of an array are all numbered, starting from 0. To add a value to an array you must specify the location in the array by putting a number in [ ].
Reading From An Array
Reading from an array is just the same as putting information in. All you have to do is to refer to the array and the number of the piece of data in the array. So if I wanted to print out the third name I could use the code:
n
echo "The third name is $names[2]";
Which would output:
The third name is Steven
Using Arrays And Loops
One of the best uses of a loop is to output the information in an array. For instance if I wanted to print out the following list of names:
Name 1 is John
Name 2 is Paul
Name 3 is Steven
Name 4 is George
Name 5 is David
I could use the following code:
$number = 5;
$x = 0;
while ($x < $number) {
$namenumber = $x + 1;
echo "Name $namenumber is $names[$x]";
++$x;
}
As you can see, I can use the variable $x from my loop to print out the names in the array. You may have noticed I am also using the variable $namenumber which is always 1 greater than $x. This is because the array numbering starts from 0, so to number the names correctly in the output I must add one to the actual value.
