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PHP TUTORIAL

BACK TO HOME Basic PHP Syntax A PHP script always starts with <?php and ends with ?>. A PHP script can be placed anywhere in the document. On servers with shorthand-support, you can start a PHP script with <? and end with ?>. For maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form. <?php ?> A PHP file must have a .php extension. A PHP file normally contains HTML tags, and some PHP scripting code. Below, we have an example of a simple PHP script that sends the text "Hello World" back to the browser: <html> <body> <?php echo "Hello World"; ?> </body> </html> 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". PHP Variables As with algebra, PHP variables are used to hold values or expressions. A variable can have a short name, like x, or a more descriptive name, like carName. Rules for PHP variable names: Variables in PHP starts with a $ sign, followed by the name of the variable The variable name must begin with a letter or the underscore character A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ) A variable name should not contain spaces Variable names are case sensitive (y and Y are two different variables) Creating (Declaring) PHP Variables PHP has no command for declaring a variable. A variable is created the moment you first assign a value to it: $myCar="Volvo"; After the execution of the statement above, the variable myCar will hold the value Volvo. Tip: If you want to create a variable without assigning it a value, then you assign it the value ofnull. Let's create a variable containing a string, and a variable containing a number: <?php $txt="Hello World!"; $x=16; ?> Note: When you assign a text value to a variable, put quotes around the value. 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, notice that we did 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. PHP Variable Scope The scope of a variable is the portion of the script in which the variable can be referenced. PHP has four different variable scopes: local global static parameter Local Scope A variable declared within a PHP function is local and can only be accessed within that function. (the variable has local scope): <?php $a = 5; // global scope function myTest() { echo $a; // local scope }  myTest(); ?> The script above will not produce any output because the echo statement refers to the local scope variable $a, which has not been assigned a value within this scope. You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared. Local variables are deleted as soon as the function is completed. Global Scope Global scope refers to any variable that is defined outside of any function. Global variables can be accessed from any part of the script that is not inside a function. To access a global variable from within a function, use the global keyword: <?php $a = 5; $b = 10; function myTest() { global $a, $b; $b = $a + $b; }  myTest(); echo $b; ?> The script above will output 15. PHP also stores all global variables in an array called $GLOBALS[index]. Its index is the name of the variable. This array is also accessible from within functions and can be used to update global variables directly. The example above can be rewritten as this: <?php $a = 5; $b = 10; function myTest() { $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b']; }  myTest(); echo $b; ?>   Static Scope When a function is completed, all of its variables are normally deleted. However, sometimes you want a local variable to not be deleted. To do this, use the static keyword when you first declare the variable: static $rememberMe; Then, each time the function is called, that variable will still have the information it contained from the last time the function was called. Note: The variable is still local to the function. Parameters A parameter is a local variable whose value is passed to the function by the calling code. Parameters are declared in a parameter list as part of the function declaration: function myTest($para1,$para2,...) { // function code } Parameters are also called arguments. We will discuss them in more detail when we talk about functions.