PHP Programming Tutorials for Beginners | PHP Variables Types

Welcome to PHPBash | Helping You to Become an Expert in PHP Programming. In this PHP Tutorial for beginners and professionals, we will learn about PHP Variables, PHP Variables Types, PHP Global Variables, php variable scope, static variable in php. As well Rules for Variable declaration.

PHP Programming Tutorials for Beginners | PHP Variables Types

This PHP tutorial covers all the topics of Basics of PHP Variable like
1. PHP Variables

2. Rules for Variable declaration

3. Creating (Declaring) PHP Variable and Assigning value
4. PHP Variable Scope & Lifetime
5. PHP Static Variables
6. Type Casting and Type Juggling in PHP
7. PHP Variable Case Sensitiveness

8. Destroying PHP Variables using unset()

9. PHP Programming Examples/Scripts on PHP Variable concept

Now let's start this tutorial with understanding PHP Variables.

PHP Variables

In computer programming, Variables are act as containers for storing data in to computer memory. Variables are named memory locations which stores data in to computer memory. The stored data in variables can be used by program for performing certain tasks. Whenever program needs variable value, it reads it from memory location.

In PHP, Variable names must be starts with Dollar Sign($) followed by the name of variable that is to be created.

Example

<?php

$msg="Welcome to PHP: First variable value";

IMPORTANT:

1. In php, Variable names are always starts with $ Sign.

2. The value of variable is considered with the most recent assignment .

3. Variables can be initialized with = ( Assignment Operator).

4. In PHP, Variables are untyped means, Variable do not know, what value will be stored in it until actual assignment of value.

5. The Type casting or data type conversion handled by PHP implicitly.

Rules for Variable declaration

As variables are named memory location, we need to specify variable_name while creating PHP variable. While creating PHP Variable, there are following Rules need to be followed:

1. Variable in PHP language must start with a Sign of Dollar ($), followed by the variable name.

2. Variable name can contain alphanumeric character as well as underscore (A-z, 0-9, _).

3. A variable name can start with a letter or underscore (_) character.

4. PHP variable can not contain spaces.

5. PHP Variable names are case sensitive. For example, $COUNT and $Count are two different variables.

6. PHP variables are created at the instance, you assign value to it.

7. IMPORTANT: One thing to be kept in mind that the variable name cannot start with a number or special symbols.

Example of some valid variable names in PHP:

$test, $value99, $test_value1, $_count etc.

Example of some Invalid variable names in PHP:

9amount, $product id, $#value1 etc.

Creating (Declaring) PHP Variable and Assigning value

The PHP variable can be created or declared with before its use. After declaration of PHP variable, = (Assignment Operator) is used for assigning a value. The assignment operator stores or assigns value present on right side to the entity present on left side like variable. The following syntax can be used to declare variable.

Syntax

<?php

$variable_name=value;

Example

<?php

// First variable: Integer

$first=10;

// Second variable: Float or Double

$second=10.10;

// Third variable: String

$third="I am String";

// Fourth variable:Boolean

$fourth=true;

// fifth variable: null

$fifth=null;

// Printing All variables

echo "First variable".$first." ";

echo "Second variable".$second." ";

echo "Third variable".$third." ";

echo "Fourth variable".$fourth." ";

echo "Fifth variable".$fifth." ";

PHP The above program will print or displays all variable values one by one on new line because we used HTML tag to break current line and start new line. In PHP, .(dot) operator is used for concatenating string value with variable value.

PHP Variable Scope & Lifetime

The scope of variable is defined as the part/area of program or script where variable is valid for access. Lifetime of variable can be defined as the Execution time during which variable is available in memory for access or use.

Basically, the Scope of variable is discussed in context of the area/part of program whereas Lifetime of variable is discussed in context of Execution time.In PHP, variables can be created anywhere in the script as per need.

Lets understand the concept of Scope and Lifetime with Example: If variable declared in a PHP function, then it will available for access only within that function(Between {...}) which is local scope. where as it will available in memory until function is executing which is Life time of variable.

There are following types of Scope of PHP variable:

1. Local Scope- Only inside Specific Function

2. Global Scope- Inside whole script/program

Based on this, There are following types of PHP variables:

1. Local Variables: The local variables are declared and created inside a function.They are accessed only within function, in which they are declared. In other words, the variables declared within functions, cant be accessed outside of that function.

In case of local variables, you can create a new variable with the same outside of that function. Both variables will be treated and used differently. Here function is block of statement written for performing particular task.

Consider following example which demonstrate use of PHP Local Variable:

<?php

$count= 10;

function test()

{

// This $count is Local variable to this function

// the variable $count outside this function

// is a completely new variable

$count = 20;

echo "Local Variable Value = $count "; //print 20 value

}

test(); // calling test() function

// printing the value of $count variable 10

echo "The value is".$count;

2. Global Variables: As described, the variable can be declared anywhere in the PHP Script. Basically, Global variables in PHP are declared outside of a function. These variables are available for access to the whole PHP Script or PHP Program. You can access them inside a function as well with help of global keyword before variable name. Another way to do this is using $GLOBALS[index]. The index is nothing but the name of the variable.

Example:

<?php

//global variable

$count= 10;

function test()

{

// Accessing global variable $count inside function with global keyword

global $count;

echo "Global Variable Value inside Function= $count "; //print 10 value

echo "Global Variable Value inside Function= $_GLOBALS['count'] ";

}

test(); // calling test() function

// printing the value of $count variable 10

echo "The Global variable value outside Function".$count;

3. Static Variables: The variables are stored in memory only during Execution of PHP program or PHP Script. Once its Execution has completed, the variables are Kicked out or flush from memory and memory is released. In simple words, variables are destroyed on function Execution complete. In some cases, we need to persist the value of variable after Execution of function is completed. so in Such scenario, PHP Static variables can be used whose value is stored even after the completion of Execution.

<?php

function static_demo()

{

STATIC $ctr= 1;

$ctr++;

echo "The value of Counter is".$ctr." ";

}

static_demo();

In this case, the output will be

Type Casting and Type Juggling in PHP

PHP is a Loosely Typed Language. It means, while declaring variable, PHP do not force to declare the data type of variable like C,C++ which are strongly typed languages. For example, here while declaring the variable $count, we did not specify the data type int or integer. PHP automatically associates the data type based on value being assigned or stored in it. so here PHP will create $count, as Integer variable.

<?php

$count= 10;

echo "The value is".$count;

IMPORTANT: IN PHP 7, The data type declaration Added which forces to declare data type of variables.

PHP Type Casting or Data Type Conversion

The PHP Typecasting or Data type conversion is process of changing or converting one type of data in to another type of data. Basically, the data type of variable defines, what types of value or data is being stored in to variable. In PHP, there are various data types like Integer,Float/Double, String, Boolean, Array, Object, Resource, Null .

so we can change the type of data type of variable by modifying the value storing in it.

Example

<?php

// First variable: Integer

$first=10;

// Second variable: Float or Double

$first=10.10;

// Third variable: String

$first="I am String";

// Fourth variable:Boolean

$first=true;

// fifth variable: null

$first=null;

// Printing All variables

echo "First variable".$first." ";

As shown in above example, data types are Type Casted automatically by PHP based on value assigned to variable.

But you can also perform Explicit Type Casting where you will manually or explicitly specify datatype in which variable should be Type casted. PHP type casting is similar to that of C language. The settype() can be used for performing Explicit Typecasting in PHP.

Loot at below example of PHP Explicit Typecasting .

<?php

$ctr = 10; // $ctr is an integer

$test = (boolean) $ctr; // $test is a boolean

Example of Explicit Typecasting with settype()

<?php

$one = "10 Pens"; // string

$two = true; // boolean

settype($one, "integer"); // $one is now 10 (integer)

settype($two, "string"); // $two is now "1" (string)

PHP Type Juggling

As PHP is loosely typed language, it does not required any explicit type definition while declaring variable. As stated earlier, the type of variable will be depend on what kind of value is stored in it. If $count is variable, and you stored String value in it. So PHP will treat or recognize $count as String Variable. If you store Integer value, PHP will recognize $count variable as Integer. This is called PHP Juggling.

<?php

$one= "10"; // $one is string

$one*= 2; // $one is now an integer (20)

$one= $one* 1.0; // $one is now a float (20.0)

$one= 5 * "5 Pens"; // $one is integer (25)

PHP Variable Case Sensitiveness

PHP is Case Sensitive language means that, $PHPBash and $PHPBASH is different variable in PHP. In PHP, variable names are case sensitive. On other hand, regarding predefined keywords like while,for,if,switch,predefined functions, user defined functions, class names are incasesensitive in PHP.

For Example:

<?php

echo "PHP Case Sensitivity Test";

ECHO "PHP Case Sensitivity Test";

Both statements in above example will produce same result.

Look at another example:

<?php

$count = 1;

echo "Count is " . $count. " ";

echo "Count is " . $COUNT. " ";

In above example, only statement will print value of $count. The second statement will not print anything because $count and $COUNT are treated as different in PHP.

Destroying PHP Variables using unset()

To destroy or unset a variable in PHP, the unset() function can be used. It needs the variable name as parameter which is to be unset or destroy.

<?php

function destroy_var()

{

global $ctr;

unset($ctr);

}

$ctr = 10;

destroy_var();

echo $ctr;

PHP Programming Examples / Scripts on PHP Variable concept

Example1: PHP Program for Addition of two numbers

<?php

$a=10;

$b=20;

$c=a+b;

echo "Addition is".$c;

Addition of two number in PHP

Example 2: PHP Program for finding greatest among two numbers

<?php

$a=10;

$b=20;

if(a>b)

{

echo "a is greater".$a;

}

else

{

echo "b is greater".$b;

}

Example 3: PHP Program for destroying variable using unset()

<?php

function test_unset()

{

unset($GLOBALS['ctr']);

}

$ctr = "Test Value";

test_unset();

Example 4: PHP Program for Different variable types

<?php

$first="I am string";

$ctr=5;

$area_circle=874.23;

echo "STRING VARIABLE: $first ";

echo "INTEGER VARIABLE: $ctr ";

echo "FLOAT VARIABLE: $area_circle ";

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