PHP Variables

Variables are data storage "containers".

A variables may be given a short name (such as x and y) or a more specific name (such as era, carname, or total volume).

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Rules for PHP variables

A variable is identified by the $ symbol, which is followed by the variable's name.
A variable name must begin with a letter or an underscore.
A number cannot be the first character in a variable name.
Only alpha-numeric characters and underscores (A-z, 0-9, and_ ) are used in variable names.
Case matters when naming variables ($age and $AGE are two distinct variables).

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Creating (Declaring) PHP Variables

A variable begins with a $ symbol in PHP and follows the variable name.

Example :-

<?php
$msg = "Welcome to PHP!";
$a = 6;
$b = 15.5;
?>

Example Explained :-

Following the execution of the preceding statements, the variable $msg will contain the value Welcome to PHP!, the variable $a will contain the value 6, and the variable $b will contain the value 15.5.

Note :- When you add a text value to an variable, surround the value with single or double quotes.

In contrast to other programming languages, PHP does not provide a command or keyword to declare a variable. It is generated or defined when you add a value to it for the first time.

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Output Variables

To display data to the browser screen, the PHP echo command is frequently used.

Example 1 :- The following example will show how to output text and a variable.

<?php
$msg = "simmanchith.com";
echo "I love $msg!";
?>

Output :-

I love simmanchith.com!

Example 2 :- The following example will produce the same output as the example above.

<?php
$msg = "simmanchith.com!";
echo "I love " . $msg . "!";
?>

Output :-

I love simmanchith.com!

Note:- We used "." symbol to concat the text and the variable name.

Example 3 :- The following example will output the sum of two variables:

<?php
$x = 5;
$y = 4;
echo $x + $y;
?>

Output :-

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PHP is a Loosely Typed Language

Depending on the value of the variable, PHP automatically assigns a data type to it. You can perform things like adding a string to an integer without raising an error since the data types aren't established in a strict sense.

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PHP Variables Scope

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

The scope of a variable refers to the area of the script where it may be the variable referenced and utilized.

PHP has three different variable scopes.

local
global
static

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Global Variable Scope

A variable declared outside of a function has a GLOBAL SCOPE and can be accessed only from outside the 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>";
?>

Output :-

Variable x inside function is: ERROR

Variable x outside function is: 5

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Local Variable Scope

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

Example :-

<?php
function myExam() {
  $e = 5; // local scope
  echo "<p>Variable e inside function is: $e</p>";
}
myExam();
// using e outside the function will generate an error
echo "<p>Variable e outside function is: $e</p>";
?>

Output :-

Variable x inside function is: 5

Variable x outside function is: ERROR

local variables are only recognized by the function in which they are defined, you can have local variables with the same name in various functions.

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PHP The global Keyword

To access a global variable from within a function, use the global keyword.

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

Example:-

<?php
$a = 5;
$b = 10;
function myExam() {
  global $a, $b;
  $b = $a + $b;
}
myExam();
echo $b; // outputs 15
?>

Output :-

PHP also keeps all global variables in a $GLOBALS[index] array. The variable's name is stored in the index. This array is also available via functions and may be used to directly update global variables.

Example:- The example above can be rewritten like this:

<?php
$a = 5;
$b = 10;
function myExam() {
  $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
}
myExam();
echo $b; // outputs 15
?>

Output :-

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PHP The static Keyword

When a function is finished/executed, all of its variables are normally erased.

However, there are occasions when we do not want a local variable to be destroyed and it also needs for the job.

Example :-

<?php
function test() {
  static $a = 0;    //  static variable
  $b = 0;   // local varaible
  echo "a = " . $a . " , b = " . &b;
  $a++;
  $b++;
}
test();
test();
test();
?>

Output :-

a = 0 , b = 0
a = 1 , b = 0
a = 2 , b = 0

A local variable will be destroyed after completing a function execution. It will be newly initialized whenever a function was called.

The static variable will then retain the information it contained the previous time the function was called each time the function is invoked.

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