PHP

PHP – Variables and Data Types

Variables are containers for storing data

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

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)

Example:

<?php

$txt="Hello world!";
$x=5;
$y=10.5;

?>

Local and Global

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.

global – Keyword

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

<?php
$x=5;
$y=10;

function myTest()
{
global $x,$y; // It takes the global variables x and y 
$y=$x+$y;
}

myTest();
echo $y; // Outputs 15
?>

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:

<?php

function myTest()
{
static $x=0; // the variable is static and it will not be deleted
echo $x;
$x++;
}

myTest(); // output is 0
echo "<br>";
myTest(); // output is 1
echo "<br>";
myTest(); // output is 2
echo "<br>";
myTest(); // output is 3
echo "<br>";
myTest(); // output is 4
?>

The result is:

0
1
2
3
4

Data Types

The types of data the variables can content.

<?php 

// STRINGS
// -------------------
$x = "Hello world!";
echo $x;
echo "<br>"; 
$x = 'Hello world!';
echo $x;

// INTEGERS
// -------------------
$x = 5985;
var_dump($x); // var_dump() function returns the data type and value of variables
echo "<br>"; 
$x = -345;    // negative number 
var_dump($x);
echo "<br>"; 
$x = 0x8C;    // hexadecimal number
var_dump($x);
echo "<br>";
$x = 047;     // octal number
var_dump($x);

// FLOATING NUMBERS
// -------------------
$x = 10.365;
var_dump($x); // var_dump() function returns the data type and value of variables
echo "<br>"; 
$x = 2.4e3;
var_dump($x);
echo "<br>"; 
$x = 8E-5;
var_dump($x);

// BOOLEANS
// -------------------
$x=true;
$y=false;

// NULL
// -------------------
$x="Hello world!";
$x=null;
var_dump($x); 

?>