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.
Syntax:
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<?php define('ConstName', 'value'); ?> |
Valid and Invalid Constant declaration:
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<?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
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<?php define('NAME', "Rexx"); echo "Hello ".NAME; ?> |
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
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<?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.
Subtraction of two numbers using constant
Ex.iii
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<?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.
Sum of two numbers and assign the result in a variable
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<?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
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<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"; ?> |
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.