Variables in php start with

PHP Variables

In this tutorial you will learn how store information in a variable in PHP.

What is Variable in PHP

Variables are used to store data, like string of text, numbers, etc. Variable values can change over the course of a script. Here're some important things to know about variables:

  • In PHP, a variable does not need to be declared before adding a value to it. PHP automatically converts the variable to the correct data type, depending on its value.
  • After declaring a variable it can be reused throughout the code.
  • The assignment operator (=) used to assign value to a variable.

In PHP variable can be declared as: $var_name = value;

In the above example we have created two variables where first one has assigned with a string value and the second has assigned with a number. Later we've displayed the variables values in the browser using the echo statement. The PHP echo statement is often used to output data to the browser. We will learn more about this in upcoming chapter.

Naming Conventions for PHP Variables

These are the following rules for naming a PHP variable:

  • All variables in PHP start with a $ 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 in PHP can only contain alpha-numeric characters and    underscores (A-z, 0-9, and _).
  • A variable name cannot contain spaces.

Note: Variable names in PHP are case sensitive, it means $x and $X are two different variables. So be careful while defining variable names.

Last update on August 19 2022 21:50:39 (UTC/GMT +8 hours)

Description

Variable is a symbol or name that stands for a value. Variables are used for storing values such as numeric values, characters, character strings, or memory addresses so that they can be used in any part of the program.

Declaring PHP variables

All variables in PHP start with a $ (dollar) sign followed by the name of the variable.

A valid variable name starts with a letter (A-Z, a-z) or underscore (_), followed by any number of letters, numbers, or underscores.

If a variable name is more than one word, it can be separated with an underscore (for example $employee_code instead of $employeecode).

'$' is a special variable that can not be assigned.

Pictorial presentation of PHP variable naming

Variables in php start with

Example : Valid and invalid PHP variables  

PHP variable name is case-sensitive

Consider the following example :

Output of the above example

Value of abc : Welcome
Value of ABC :

In the above example, the different capitalization schemes make for different variables.

PHP is a loosely type language

In a language such as C, C++, and Java the programmer must declare the name and type of the variable before use it. In PHP the type of the variable does not need to be declared before use it  because types are associated with values rather than variables. As a result, a variable can change the type of its value as much as we want.

As previously mentioned you don't need to declare variables or their type before using them in PHP. In the following example, none of the variables are declared before they are used, the fact is $height is floating number and $width is an integer. 

PHP variables: Assigning by Reference

PHP (from PHP4) offers another way to assign values to variables: assign by reference. This means that the new variable simply points the original variable. Changes to the new variable affect the original, and vice a verse.

Consider the following example:

';
echo $foo;
?>

Output:

my bob
  my bob

PHP variable variables

You know how to declare variables in PHP. But what if you want the name your variable is a variable itself? In PHP, you have Variable Variables, so you may assign a variable to another variable.

In the following example at line no. 2, we declared a variable called $v which stores the value 'var1' and in line no. 4, "var1" is used as the name of a variable by using two dollar signs. i.e. $$v.

Therefore there are two variables now. $v which stores the value "var1" where as $$v which stores the value var2. At this point $$v and $var1 are equal, both store the value "var2".

Example:


PHP Variables Scope

In PHP, variables can be declared anywhere in the script. We declare the variables for a particular scope. There are two types of scope, the local scope where variables are created and accessed inside a function and global scope where variables are created and accessed outside a function.

Example:

";
echo "The value of y is :  $y"."
"; } var_scope(); echo "The value of x is : $x"."
"; echo "The value of y is : $y "; ?>

In the above script there are two variables $x and $y and a function var_scope(). $x is a global variable since it is declared outside the function and $y is a local variable as it is created inside the function var_scope(). At the end of the script var_scope() function is called, followed by two echo statements. Lets see the output of the script :

  The value of x is :
  The value of y is :  20
  The value of x is :  10
  The value of y is : 

There are two echo statements inside var_scope() function. It prints the value of $y as it is the locally declared and can not prints the value of $x since it is created outside the function.

The next statement of the script prints the value of $x since it is global variable i.e. not created inside any function.

The last echo statement can not prints the value of $y since it is local variable and it is created inside the function var_scope() function.

View the example in the browser

The global keyword

We have already learned variables declared outside a function are global. They can be accessed anywhere in the program except within a function.

To use these variables inside a function the variables must be declared global in that function. To do this we use the global keyword before the variables. Consider the following the example :

Example:


In the above example $x, $y, $z, $xyz have initialized with 2, 4, 5, 0. Inside the multiple() function we declared $x, $y, $z, $xyz as global. Therefore all reference of each variable will refer to global version. Now call multiple() anywhere in the script and the variable $xyz will print 40 as it is already referred as global.

View the example in the browser

PHP static variables

Normally when a function terminates, all of its variables loose its values. Sometimes we want  to  hold these values for the further job. Generally, those variables which hold the values are called static variables inside a function. To do this we must write the keyword "static" in front of  those  variables. Consider the following example without a static variable. 

Example: without static variable

";
test_variable();
echo "
"; test_variable(); ?>

In the above script the function test_variable() is useless as the last statement $x = $x +1 can not increase the value of $x since every time it is called $x sets to 1 and print 1.

Output:

  1
  1
  1

View the example in the browser

To overcome the problem of the above script $x can be declared as static. See the following example.

Example: with static variable

";
test_count();
echo "
"; test_count(); ?>

Output:

  1
  2
  3

View the example in the browser

PHP : Reserve Words

The words in the following table are reserve words and cannot be used as constants, class names, function or method names. You can use them as variable names, but do not use as variable names to avoid confusion.

PHP Keywords

abstract (as of PHP 5) andarray()asbreak
case catch (as of PHP 5) cfunction ( PHP 4 only) class clone (as of PHP 5)
const continue declare default do
else elseif enddeclare endfor endforeach
endif endswitch endwhile extends final (as of PHP 5)
for foreach function global goto (as of PHP 5.3)
if implements (as of PHP 5) interface (as of PHP 5) instanceof (as of PHP 5) private (as of PHP 5)
namespace (as of PHP 5.3) new old_function (PHP 4 only) or throw (as of PHP 5)
protected (as of PHP 5) public (as of PHP 5) static switch xor
try (as of PHP 5) use var while  

Compile-time constants

__CLASS__ _DIR__ (as of PHP 5.3) _FILE_ __LINE__ __FUNCTION__
__METHOD__ __NAMESPACE__ (as of PHP 5.3)      

Language constructs

die() echo() empty() exit() eval()
include() include_once() isset() list() require()
require_once() return() print() unset()  

Practice here online :

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Next: Echo statement

What is a PHP variable?

PHP VARIABLES: A variable in PHP is a name of memory location that holds data. In PHP, a variable is declared using $ sign followed by variable name. The main way to store information in the middle of a PHP program is by using a variable.

Can a variable in PHP start with a number?

A variable name must start with a letter or the underscore character _ . A variable name cannot start with a number. A variable name in PHP can only contain alpha-numeric characters and underscores ( A-z , 0-9 , and _ ). A variable name cannot contain spaces.

What is variable type in PHP?

PHP has a total of eight data types which we use to construct our variables − Integers − are whole numbers, without a decimal point, like 4195. Doubles − are floating-point numbers, like 3.14159 or 49.1. Booleans − have only two possible values either true or false.

Which is the correct way to declare a PHP variable?

Declaring PHP variables All variables in PHP start with a $ (dollar) sign followed by the name of the variable. A valid variable name starts with a letter (A-Z, a-z) or underscore (_), followed by any number of letters, numbers, or underscores.