PHP Constants: PHP Constants are the identifiers that remain the same. Usually, it does not change during the execution of the script. They are case-sensitive. By default, constant identifiers are always uppercase. Usually, a Constant name starts with an underscore or a letter which is followed by a number of letters and numbers. They are no need to write a constant with the $ sign. The constant() function is used to return the value of a constant.
Example:
PHP
<?php    define("Hello", "Welcome to neveropen.com!");    echo Hello; ?> |
Output:
Welcome to neveropen.com!
PHP Variables: A PHP variable is a name given to a memory address that holds data. The basic method to declare a PHP variable is by using a $ sign which is followed by the variable name. A variable helps the PHP code to store information in the middle of the program. If we use a variable before it is assigned then it already has a default value stored in it. Some of the data types that we can use to construct a variable are integers, doubles, and boolean.
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Example:
PHP
<?php    $txt = "Hello from neveropen!";    $x = 5;    $y = 10.5;    echo $txt;    echo "<br>";    echo $x;    echo "<br>";    echo $y; ?> |
Output:
Hello from neveropen! 5 10.5
Difference between PHP Constants and PHP Variables
| PHP Constants | PHP Variables |
| In PHP constants there is no need to use $ sign. | In PHP Variables the $ sign is been used. |
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The data type of PHP constant cannot be changed during the execution of the script. |
The data type of the PHP variable can be changed during the execution of the script. |
| A PHP constant once defined cannot be redefined. | A PHP variable can be undefined as well as can be redefined. |
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We can not define a constant using any simple assignment operator rather it can only be defined using define(). |
We can define a variable using a simple assignment operation(=). |
| Usually, constants are written in numbers. | On the other hand, variables are written in letters and symbols. |
| PHP constants are automatically global across the entire script. | PHP variables are not automatically global in the entire script. |
| PHP constant is comparatively slower than PHP variable | A PHP variable is comparatively faster than the PHP constant |
