PHP VARIABLES

What is PHP Variables ?

Variables are like the "containers" for storing information.

A variable can have a short name (like a and b) or a more descriptive name (age, username, user_name).

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($age and $AGE are two different variables)
• PHP variable names are case-sensitive.
• Example: $a=30, $name=”Lopa”.

PHP is a Loosely Typed Language

In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.

But 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.

Scope of PHP Variables

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

1)Global  Scope

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

Example:

<?php
$x = 5; // global scope

function myTest() {
    // using x inside this function will generate an error
    echo "<p>Variable x inside function is: $x</p>";
} 
myTest();

echo "<p>Variable x outside function is: $x</p>";
?>

2)Local  Scope

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

Example:

<?php
function myTest() {
    $x = 5; // local scope
    echo "<p>Variable x inside function is: $x</p>";
}
myTest();

// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>

3)Static Scope

A variable declared as static called as static variable and that will not lose its value when the function exits and will still hold that value should the function be called again.

You can declare a variable to be static simply by placing the keyword STATIC in front of the variable name.

Syntax: STATIC $x=0;

Example:

<?php
function myTest() {
    static $x = 5; // local scope
    echo "<p>Variable x inside function is: $x</p>";
}
myTest();

// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>

Naming Rule of a Variable:

Rules for naming a variable is −

·        Variable names must begin with a letter or underscore character.

·        A variable name can consist of numbers, letters, underscores but you cannot use characters like + , - , % , ( , ) . & , etc

There is no size limit for variables.

Data Types in PHP

The values assigned to a PHP variable may be of different data types including simple string and numeric types to more complex data types like arrays and objects.

PHP supports total eight primitive data types: Integer, Floating point number or Float, String, Booleans, Array, Object, resource and NULL.

These data types are used to construct variables. 

1) PHP Integers

They are whole numbers, without a decimal point, like  (..., -2, -1, 0, 1, 2, ...). They are the simplest type and they correspond to simple whole numbers, both positive and negative.

Integers can be assigned to variables, or they can be used in expressions, like so –

$var1=12345;

$another_var1=-12345+12345;

Integer can be specified in decimal (base 10), octal (base 8), and hexadecimal (base 16) format.

Integer can be optionally preceded by a sign –ve or +ve.

Decimal format is the default, octal integers are specified with a leading 0, and hexadecimals have a leading 0x.

For most common platforms, the largest integer is (2**31 . 1) (or 2,147,483,647), and the smallest (most negative) integer is . (2**31 . 1) (or .2,147,483,647).

<?php

$a=123; //decimal number

var_dump($a);

echo “<br>”;

$b=-123; //a negative  number

var_dump($b);

echo “<br>”;

$c=0x1A; //hexadecimal number

var_dump($c);

echo “<br>”;

$d=0123; //octal number

var_dump($d);

echo “<br>”;

?>

PHP Floating Point Numbers or Doubles

They like 1.14159 or 45.1.

By default, doubles print with the minimum number of decimal places needed. For example,

<?php

$a=2.2888800;

$b=2.2888800;

$new=$a+ $b;

print(“$a + $b= $new <br>”);

?>

Output of above is 2.28888 + 2.21112=4.5

 

Floating point numbers (also known as "floats", "doubles", or "real numbers") are decimal or fractional numbers.

Examples:

<?php

$a=1.234;

var_dump($a);

echo “<br>”;

$b=10.2e3;

var_dump($b);

echo “<br>”;

$c=4E-10;

var_dump($c);

echo “<br>”;

 

3)PHP Booleans

They have only two possible values either true or false. PHP provides a couple of constants especially for use as Booleans: TRUE and FALSE, which can be used like so

If(TRUE)

print(“this will always print<br>”);

else

print(“this will never print<br>”);

 

Booleans are like a switch it has only two possible values either 1(true) or 0(false).

$show_booleans = true;

var_dump($show_booleans);

echo “<br>”;

Interpreting other types as Booleans

Here are the rules for determine the "truth" of any value not already of the Boolean type −

·        If the value is a number, it is false if exactly equal to zero and true otherwise.

·        If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.

·        Values of type NULL are always false.

·        If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.

·        Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).

·        We Don't use double as Booleans.

4)PHP Arrays

An array is a variable that can hold more than one value at a time. It is useful to aggregate a series of related items together, for example a set of country or city names.

An array is formally defined as an indexed collection of data values. Each index (also known as the key) of an array is unique and references a corresponding value.

Example:

<?php

$name=array(“Ram”,”Hari”,”Gopal”);

var_dump($name);

echo “<br>”;

$title=array(

   “Ram”=>”Mishra”,

   “Hari”=>”Das”,

   “Ram”=>”Mishra”

);

var_dump($title);

?>

5)PHP Strings

Strings are sequences of characters, where every character is the same as a byte.

A string can hold letters, numbers, and special characters and it can be as large as up to 2GB (2147483647 bytes maximum). The simplest way to specify a string is to enclose it in single quotes (e.g. 'Hello world!'), however you can also use double quotes ("Hello world!").

<?php

$a=”Hello World!”;

echo $a;

echo “<br>”;

$b=’Plz stay here,I\’ll be back again’;

echo $b;

echo “<br>”;

6)PHP Objects

An object is a data type that not only allows storing data but also information on, how to process that data. An object is a specific instance of a class which serve as templates for objects. Objects are created based on this template via the new keyword.

Every object has properties and methods corresponding to those of its parent class. Every object instance is completely independent, with its own properties and methods, and can thus be manipulated independently of other objects of the same class.

Here's a simple example of a class definition followed by the object creation.

Example:

<?php

//class definition

class newclass {

public $str=”Hello World!”;//properties

function show_new(){

return $this->str;

}

}

$msg=new newclass;

var_dump($message);

?>

7)PHP NULL

The special NULL value is used to represent empty variables in PHP. A variable of type NULL is a variable without any data. NULL is the only possible value of type null.

<?php

$a=NULL;

var_dump($a);

echo “<br>”;

$b=”Hello World!”;

$b=NULL;

var_dump($b);

?>

When a variable is created without a value in PHP like $var; it is automatically assigned a value of null. Many novice PHP developers mistakenly considered both $var1 = NULL; and $var2 = ""; are same, but this is not true. Both variables are different — the $var1 has null value while $var2 indicates no value assigned to it.

8)PHP Resources

A resource is a special variable, holding a reference to an external resource.

Resource variables typically hold special handlers to opened files and database connections.

<?php

$handle=fopen(“note.txt”,”r”);

var_dump($handle);

echo “<br>”;

// Connect to MySQL database server with default setting

$link=mysql_connect(“localhost”, “root”, “”);

var_dump($link);

?>