3/20/15

PHP Constant



Constant in PHP

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

Rules for defining constant

Constants are defined using PHP’s define( ) function, which accepts two arguments:
The name of the constant, and its value.
Constant name must follow the same rules as variable names, with one exception the “$” prefix is not required for constant names.
Here’s an example of defining and using a constant.
Syntax:
  <?php  
  define('ConstName', 'value');
  ?>

Valid and Invalid Constant declaration:

<?php
   //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");
 define('@SUM',ONE+TWO);
 ?> 

Create a constant and assign your name

Ex i
  <?php  
  define('NAME', "phpTpoint");
  echo  NAME;
  ?>
   Output : phpTpoint
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

Write a Program to Print the Sum of two numbers using constant

Ex.ii
  <?php  
  define('ONE', 100);
  define('TWO', 100);
  define('SUM',ONE+TWO);
  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.

Write a Program to Print the Subtraction of two numbers using constant

Ex.iii
  <?php  
  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.

Write a Program to Print the Sum of two numbers and assign the result in variable not in constant

Ex.iv
  <?php  
  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

Ex.v
<h2>USD/EUR Currency Conversion</h2>
<?php
//define exchange rate
//1.00 USD= 0.80 EUR
define('EXCHANGE_RATE',0.80);

//define number of dollars
$dollars=150;

//perform conversion and print result
$euros=$dollars*EXCHANGE_RATE;
echo "$dollars USD is equivalent to :$euros EUR";
?>  
Output :

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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