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PHP Constant

Constant in PHP

  1. Constants are PHP container that remain constant and never change
  2. Constants are used for data that is unchanged at multiple place within our program.
  3. Variables are temporary storage while Constants are permanent.
  4. Use Constants for values that remain fixed and referenced multiple times.

Rules for defining constant

  1. Constants are defined using PHP's define( ) function, which accepts two arguments: The name of the constant, and its value.
  2. Constant name must follow the same rules as variable names, with one exception the "$" prefix is not required for constant names.


define('ConstName', 'value');


Valid and Invalid Constant declaration:

//valid constant names 
define('ONE', "first value");
define('TWO', "second value");
define('SUM 2',ONE+TWO);
//invalid constant names
define('1ONE', "first value");
define(' TWO', "second value");


Create a constant and assign your name

define('NAME', "Rexx");
echo  "Hello ".NAME;

Output Hello Rexx

In the above example We define a constant using define( ) function. first argument for name of constant and second for its value="phptpoint". Now we print the value. Pass name of constant inside print statement Output will become

Sum of two numbers using constant

define('ONE', 100);
define('TWO', 100);
print "Sum of two constant=".SUM;


Output Sum of two constant = 200

In the above example We declare three constant of name=(ONE,TWO,SUM). First Add the value of two constant. Now sum of these two value work as a value for third define constant(SUM). Now pass $sum inside print it will show the sum of two number.

Subtraction of two numbers using constant


define('X', 1000);
define('Y', 500);
define('Z',X - Y);
print "Subtraction of given number =".Z;


Output Subtraction of given number = 500

In the above example We define three constant with name(X,Y,Z). First subtract the value of two defined constant . Now result of these two value work as a value for third define constant(Z). Pass Z inside print so it will show the subtraction of two value.

Sum of two numbers and assign the result in a variable

define('ONE', 100);
define('TWO', 100);
$res= ONE+TWO;
print "Sum of two constant=".$res;

Output Sum of two constant = 200

In the above example We define two constant with name(one,two) and value(100,100) respectively. $res variable is also define. Now we perform addition of two defined constant value and result store in a variable($res = one+two;). To print the result pass $res inside print statement.

Building a Dollars-to-Euros Converter

<h2>USD/EUR Currency Conversion</h2>


//define exchange rate
//1.00 USD= 0.80 EUR

//define number of dollars

//perform conversion and print result

echo "$dollars USD is equivalent to :$euros EUR";



USD/EUR Currency Conversion

150 USD is equivalent to :120 EUR

if you have been following along, the script should be fairly easy to understand. It begins by defining a constant named "EXCHANGE_RATE" which surprise, surprise stores the dollar-to-euro exchange rate(assumed here at 1.00 USD to 0.80 EUR). Next, it defines a variable named "$dollars" to hold the number of dollars to be converted, and then it performs an arithmetic operation using the * operator, the "$dollars" variable, and the "EXCHANGE_RATE" constant to return the equivalent number of euros. This result is then stored in a new variable named "$euros" and printed to the Web page.

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