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PHP Variables

Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive, so $Abc is different from $abc.

A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.


Comment is a part of your PHP code that will not be translated by the PHP engine. You can use it to write documentation of your PHP script describing what the code should do. A comment can span only for one line or span multiple line.

PHP support three kinds of comment tags :

  1. // This is a one line comment
  2. # This is a Unix shell-style comment. It's also a one line comment
  3. /* ..... */ Use this multi line comment if you need to.

* For all PHP code in this website I will use the comment by gray text and result of the code show you with italic character.


$a="Hello PHP ";
// valid
$Var_is-123="World"; // valid
$num=12; // valid
$_num='130 miles'; // valid
$123Start="Go Now"; // invalid, starts with number

PHP supports eight primitive types.

  • boolean : expresses truth value, TRUE or FALSE. Any non zero values and non empty string are also counted as TRUE.
  • integer : round numbers (-5, 0, 10, 2364, ...)
  • float : floating-point number or 'double' (0.9238, 26.0, ...)
  • string : "Hello World", 'PHP MySQL', etc.
  • array
  • object
  • resource ( one example is the return value of mysql_connect() function)
  • NULL

Output a String

Strings are probably what you will use most in your PHP script. To declare a string in PHP you can use double quotes ( " ) or single quotes ( ' ). There are some differences you need to know about using these two.

$today = 'Friday';

echo "Today is $today <br>"; // Result : Today is Friday
echo 'Today is $today <br>'; // Result : Today is $today <br>
echo "Today is".$today."<br>"; // Result : Today is Friday. Use "." between String and Variable
// three lines above. <br> is HTML tag that means to make a line break



Operators in PHP are using between two variables or between variable and value.

%Modulus (division remainder)5%2

Assignment Operators

OperatorExampleIs The Same As


In PHP an array can have numeric key, associative key or both. The value of an array can be of any type. To create an array use the array() language construct.


$x=array(1, "test", 35, 434, "test2", 6);

/*$x has 6 values. They are indexing by the number starting by 0, 1, 2,... and you can output them by using these index number as $x[0], $x[1], $x[2],...*/
echo $x[0]; // Result : 1
echo $x[4]; // Result : test2

$y = array("hello" => "World", 1 => "PHP is easy", 45 => 100);
/* $y has 3 values. They are indexing by strings and number, use => to fix the index and value. */

echo $y['hello']; // Result : World. You can use ' or " for the index using strings in [] signs.
echo $y[45]; // Result : 100

// these lines below shows you can set an array variable by directly.

PHP Superglobals

Superglobals are variables that available anywhere in the program code. They are :

  • $_SERVER
    Variables set by the web server or otherwise directly related to the execution environment of the current script. One useful variable is $_SERVER['REMOTE_ADDR'] which you can use to know you website visitor's IP address

    echo "Your computer IP is ";
    echo $_SERVER['REMOTE_ADDR'];

  • $_GET
    Variables provided to the script via HTTP GET. You can supply GET variables into a PHP script by appending the script's URL like this :
    or set the a form method as method="get"

    The target file (test.php) when the URL is

    $b=$_GET['a']; // make $b receive the variable from $a at GET method.
    echo $b; // Result : 100

  • $_POST
    Variables provided to the script via HTTP POST. These comes from a form which set method="post"
  • $_COOKIE
    Variables provided to the script via HTTP cookies.
  • $_FILES
    Variables provided to the script via HTTP post file uploads.
  • $_ENV
    Variables provided to the script via the environment.
    Variables provided to the script via the GET, POST, and COOKIE input mechanisms, and which therefore cannot be trusted. It's use the appropriate $_POST or $_GET from your script instead of using $_REQUEST so you will always know that a variable comes from POST or GET.
    Contains a reference to every variable which is currently available within the global scope of the script.

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