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." ";

echo $x." ";

echo $y." ";

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 "Test variables inside the function:";

echo "Variable x is: $x";

echo " ";

echo "Variable y is: $y";

}

myTest();

echo "Test variables outside the function:";

echo "Variable x is: $x";

echo " ";

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();