Basic PHP

Basic PHP

What You Should Already Know

Before you continue you should have a basic understanding of the following:
HTML/XHTML
JavaScript

If you want to study these subjects first, find the tutorials on our Home page.

What is PHP?

PHP stands for PHP: Hypertext Preprocessor
PHP is a server-side scripting language, like ASP
PHP scripts are executed on the server
PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
PHP is an open source software
PHP is free to download and use
What is a PHP File?
PHP files can contain text, HTML tags and scripts
PHP files are returned to the browser as plain HTML 
PHP files have a file extension of “.php”, “.php3”, or “.phtml”
What is MySQL?
MySQL is a database server
MySQL is ideal for both small and large applications
MySQL supports standard SQL
MySQL compiles on a number of platforms
MySQL is free to download and use
PHP + MySQL
PHP combined with MySQL are cross-platform (you can develop in Windows and serve on a Unix platform)
Why PHP?
PHP runs on different platforms (Windows, Linux, Unix, etc.)
PHP is compatible with almost all servers used today (Apache, IIS, etc.)
PHP is FREE to download from the official PHP resource: http://www.php.net
PHP is easy to learn and runs efficiently on the server side
Where to Start?
To get access to a web server with PHP support, you can:
Install Apache (or IIS) on your own server, install PHP, and MySQL
Or find a web hosting plan with PHP and MySQL support
What do you Need?
If your server supports PHP you don’t need to do anything.
Just create some .php files in your web directory, and the server will parse them for you. Because it is free, most web hosts offer PHP support.
However, if your server does not support PHP, you must install PHP.
Here is a link to a good tutorial from PHP.net on how to install PHP5: http://www.php.net/manual/en/install.php
Download PHP
Download PHP for free here: http://www.php.net/downloads.php
Download MySQL Database
Download MySQL for free here: http://www.mysql.com/downloads/index.html
Download Apache Server
Download Apache for free here: http://httpd.apache.org/download.cgi

Basic PHP Syntax
A PHP scripting block always starts with . A PHP scripting block can be placed anywhere in the document.
On servers with shorthand support enabled you can start a scripting block with .
For maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form.

A PHP file normally contains HTML tags, just like an HTML file, and some PHP scripting code.
Below, we have an example of a simple PHP script which sends the text “Hello World” to the browser:

Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.
There are two basic statements to output text with PHP: echo and print. In the example above we have used the echo statement to output the text “Hello World”.
Note: The file must have a .php extension. If the file has a .html extension, the PHP code will not be executed.

Comments in PHP
In PHP, we use // to make a single-line comment or /* and */ to make a large comment block.

Variables in PHP
Variables are used for storing a values, like text strings, numbers or arrays.
When a variable is declared, it can be used over and over again in your script.
All variables in PHP start with a $ sign symbol.
The correct way of declaring a variable in PHP:
$var_name = value;
New PHP programmers often forget the $ sign at the beginning of the variable. In that case it will not work.
Let’s try creating a variable containing a string, and a variable containing a number:

PHP is a Loosely Typed Language
In PHP, a variable does not need to be declared before adding a value to it.
In the example above, you see that you do not have to tell PHP which data type the variable is.
PHP automatically converts the variable to the correct data type, depending on its value.
In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.
In PHP, the variable is declared automatically when you use it.

Naming Rules for Variables
A variable name must start with a letter or an underscore “_”
A variable name can only contain alpha-numeric characters and underscores (a-z, A-Z, 0-9, and _ )
A variable name should not contain spaces. If a variable name is more than one word, it should be separated with an underscore ($my_string), or with capitalization ($myString)

String Variables in PHP
String variables are used for values that contains characters.
In this chapter we are going to look at the most common functions and operators used to manipulate strings in PHP.
After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
Below, the PHP script assigns the text “Hello World” to a string variable called $txt:

The output of the code above will be:
Hello World
Now, lets try to use some different functions and operators to manipulate the string.

The Concatenation Operator
There is only one string operator in PHP.
The concatenation operator (.)  is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:

The output of the code above will be:
Hello World! What a nice day!
If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string (a space character), to separate the two strings.

The strlen() function
The strlen() function is used to return the length of a string.
Let’s find the length of a string:

The output of the code above will be:
12
The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string).

The strpos() function
The strpos() function is used to search for character within a string.
If a match is found, this function will return the position of the first match. If no match is found, it will return FALSE.
Let’s see if we can find the string “world” in our string:

The output of the code above will be:
6
The position of the string “world” in our string is position 6. The reason that it is 6 (and not 7), is that the first position in the string is 0, and not 1.

Complete PHP String Reference
For a complete reference of all string functions, go to our complete PHP String Reference.
The reference contains a brief description, and examples of use, for each function!
PHP Operators
This section lists the different operators used in PHP.

Arithmetic Operators
Operator
Description
Example
Result
+
Addition
x=2
x+2
4
–
Subtraction
x=2
5-x
3
*
Multiplication
x=4
x*5
20
/
Division
15/5
5/2
3
2.5
%
Modulus (division remainder)
5%2
10%8
10%2
1
2
0
++
Increment
x=5
x++
x=6
—
Decrement
x=5
x–
x=4

Assignment Operators
Operator
Example
Is The Same As
=
x=y
x=y
+=
x+=y
x=x+y
-=
x-=y
x=x-y
*=
x*=y
x=x*y
/=
x/=y
x=x/y
.=
x.=y
x=x.y
%=
x%=y
x=x%y

Comparison Operators
Operator
Description
Example
==
is equal to
5==8 returns false
!=
is not equal
5!=8 returns true

is not equal
58 returns true
>
is greater than
5>8 returns false
<
is less than
5=
is greater than or equal to
5>=8 returns false
<=
is less than or equal to
5<=8 returns true

Logical Operators
Operator
Description
Example
&&
and
x=6
y=3
(x 1) returns true
||
or
x=6
y=3
(x==5 || y==5) returns false
!
not
x=6
y=3
!(x==y) returns true

Conditional Statements
Very often when you write code, you want to perform different actions for different decisions.
You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:
if statement – use this statement to execute some code only if a specified condition is true
if…else statement – use this statement to execute some code if a condition is true and another code if the condition is false
if…elseif….else statement – use this statement to select one of several blocks of code to be executed
switch statement – use this statement to select one of many blocks of code to be executed

The if Statement
Use the if statement to execute some code only if a specified condition is true.
Syntax
if (condition) code to be executed if condition is true;
The following example will output “Have a nice weekend!” if the current day is Friday:

Notice that there is no ..else.. in this syntax. The code is executed only if the specified condition is true.

The if…else Statement
Use the if….else statement to execute some code if a condition is true and another code if a condition is false.
Syntax
if (condition)
  code to be executed if condition is true;
else
  code to be executed if condition is false;
Example
The following example will output “Have a nice weekend!” if the current day is Friday, otherwise it will output “Have a nice day!”:

If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:

<?php
$d=date("D");
if ($d=="Fri")
  {
  echo "Hello!
“;
  echo “Have a nice weekend!”;
  echo “See you on Monday!”;
  }
?>

The if…elseif….else Statement
Use the if….elseif…else statement to select one of several blocks of code to be executed.
Syntax
if (condition)
  code to be executed if condition is true;
elseif (condition)
  code to be executed if condition is true;
else
  code to be executed if condition is false;
Example
The following example will output “Have a nice weekend!” if the current day is Friday, and “Have a nice Sunday!” if the current day is Sunday. Otherwise it will output “Have a nice day!”:

The PHP Switch Statement
Use the switch statement to select one of many blocks of code to be executed.
Syntax
switch (n)
{
case label1:
  code to be executed if n=label1;
  break;
case label2:
  code to be executed if n=label2;
  break;
default:
  code to be executed if n is different from both label1 and label2;
}
This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.
Example

What is an Array?
A variable is a storage area holding a number or text. The problem is, a variable will hold only one value.
An array is a special variable, which can store multiple values in one single variable.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:
$cars1=”Saab”;
$cars2=”Volvo”;
$cars3=”BMW”;
However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The best solution here is to use an array!
An array can hold all your variable values under a single name. And you can access the values by referring to the array name.
Each element in the array has its own index so that it can be easily accessed.
In PHP, there are three kind of arrays:
Numeric array – An array with a numeric index
Associative array – An array where each ID key is associated with a value
Multidimensional array – An array containing one or more arrays

Numeric Arrays
A numeric array stores each array element with a numeric index.
There are two methods to create a numeric array.
1. In the following example the index are automatically assigned (the index starts at 0):
$cars=array(“Saab”,”Volvo”,”BMW”,”Toyota”);
2. In the following example we assign the index manually:
$cars[0]=”Saab”;
$cars[1]=”Volvo”;
$cars[2]=”BMW”;
$cars[3]=”Toyota”;
Example
In the following example you access the variable values by referring to the array name and index:

The code above will output:
Saab and Volvo are Swedish cars.

Associative Arrays
An associative array, each ID key is associated with a value.
When storing data about specific named values, a numerical array is not always the best way to do it.
With associative arrays we can use the values as keys and assign values to them.
Example 1
In this example we use an array to assign ages to the different persons:
$ages = array(“Peter”=>32, “Quagmire”=>30, “Joe”=>34);
Example 2
This example is the same as example 1, but shows a different way of creating the array:
$ages[‘Peter’] = “32”;
$ages[‘Quagmire’] = “30”;
$ages[‘Joe’] = “34”;
The ID keys can be used in a script:

The code above will output:
Peter is 32 years old.

Multidimensional Arrays
In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.
Example
In this example we create a multidimensional array, with automatically assigned ID keys:
$families = array
  (
  “Griffin”=>array
  (
  “Peter”,
  “Lois”,
  “Megan”
  ),
  “Quagmire”=>array
  (
  “Glenn”
  ),
  “Brown”=>array
  (
  “Cleveland”,
  “Loretta”,
  “Junior”
  )
  );
The array above would look like this if written to the output:
Array
(
[Griffin] => Array
  (
  [0] => Peter
  [1] => Lois
  [2] => Megan
  )
[Quagmire] => Array
  (
  [0] => Glenn
  )
[Brown] => Array
  (
  [0] => Cleveland
  [1] => Loretta
  [2] => Junior
  )
)
Example 2
Lets try displaying a single value from the array above:
echo “Is ” . $families[‘Griffin’][2] .
” a part of the Griffin family?”;
The code above will output:
Is Megan a part of the Griffin family?