Constants in PHP language

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Constants in PHP language

Notes:

PHP Constants
Variable:
Variable is a named memory location, whose value may change during the execution of a program.

Constant:
Constant is a named memory location, whose value never changes during the execution of a program.
I.e. constants stay constant whereas variables vary.

Declaring a variable or a constant: means allocating a memory location for some data

Initializing a variable or a constant: means putting an initial data value within that allocated memory location

Assigning a variable or a constant: means putting a new data value within that allocated memory location

Syntax:

// declaration and initialization of a constant
const NAME_OF_CONSTANT = value;

// declaration and initialization of a constant
define(“NAME_OF_CONSTANT”,value, bool case_insensitive) : bool;

Note:
No comma separated variable or constants allowed, like in other languages

Variables must be initialized, before using them.
Constants must and should be initialized, when they are declared or defined

While accessing a variable directly within a string, it’s recommended to enclose a variable within {}
Constants are not recognized when used inside a string.

Example code:

<?php

/*

$playerScore = 0;
echo $playerScore," ";

$playerScore = 20;
echo $playerScore," ";
echo " ";

const PI = 3.142;
echo PI," ";

// PI = 4.142; // error

define("SCREEN_WIDTH",600);
echo SCREEN_WIDTH," ";

// SCREEN_WIDTH = 400; // error

*/

/*

const PI = 3.142;
echo PI," ";
// echo pi," "; // case sensitive

define("SCREEN_WIDTH",600,true);
echo SCREEN_WIDTH," ";
echo screen_width," ";
echo sCREEN_width," ";
echo screen_WIDTH," ";
*/

/*

$isGameOver;
$isGameOver=true;
echo $isGameOver," ";

const PI = 3.142;
echo PI," ";
*/

$isGameOver=true;
echo "is game over = {$isGameOver}"," ";

const PI = 3.142;
echo "PI value is = {PI}"," ";

?>

Interview Questions:

1. PHP stands for ______________
a. Hypertext Preprocessor
b. Preprocessor Hypertext
c. Personal Home Processor
d. Personal Hypertext processor
Ans: a

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