PHP Eclipse 102: Variables

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PHP Basic 102 Using Eclipse IDE - Variables

INTRODUCTIONS

This tutorial is adapted from: http://www.w3schools.com/PHP/php_variables.asp

STEPS

0) Preparation

Create a subfolder in your project and name it as 102.

1) Using Variables (Declare and Display).

As with algebra, PHP variables can be used to hold values (x=5) or expressions (z=x+y).

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).

Rules for PHP variables:

• A variable starts with the $ sign, followed by the name of the variable
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case sensitive ($y and $Y are two different variables)

PHP has no command for declaring a variable. A variable is created the moment you first assign a value to it.

usingvariables.php

<?php //declare variables $txt="Hello world!"; $x=5; $y=10.5; //display variables echo $txt."<br/>"; echo $x."<br/>"; echo $y."<br/>"; ?>

2) Variable Scopes (Local and Global)

In PHP, variables can be declared anywhere in the script.

The scope of a variable is the part of the script where the variable can be referenced/used.

PHP has three different variable scopes:

• local
• global
• static

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function.

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function.

variablescopes.php

<?php $x=5; // global scope function myTest() {   $y=10; // local scope   echo "<p>Test variables inside the function:</p>";   echo "Variable x is: $x";   echo "<br>";   echo "Variable y is: $y"; } myTest(); echo "<p>Test variables outside the function:</p>"; echo "Variable x is: $x"; echo "<br>"; echo "Variable y is: $y"; ?>

3) Global Keyword

The global keyword is used to access a global variable from within a function.

To do this, use the global keyword before the variables (inside the function).

globalkeyword.php

<?php $x=5; $y=10; function myTest() {   global $x,$y;   $y=$x+$y; } myTest(); echo $y; // outputs 15 ?>

4) GLOBALS Array

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.

globals.php

<?php $x=5; $y=10; function myTest() {   $GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y']; } myTest(); echo $y; // outputs 15 ?>

5) Static Keyword

Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job.

To do this, use the static keyword when you first declare the variable.

statickeyword.php

<?php function myTest() {   static $x=0;   echo $x;   $x++; } myTest(); myTest(); myTest(); ?>

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