<?php interface AnimalInterface { public function makeSound(); } class Dog implements AnimalInterface { public function makeSound() { echo "Woof! <br />"; } } class Cat implements AnimalInterface { public function makeSound() { echo "Meow! <br />"; } } $myObj1 = new Dog(); $myObj1-> makeSound(); $myObj2 = new Cat(); $myObj2->makeSound(); ?>

If the current day is Sunday the code will output "I don't worl."

<?php
$d = date("D");
if ($d == "Sun"){
    echo "I don't work". ".";
} 
?>

If the current hour is less than 20, the code will output "I am going to sleep"

<?php
$t = date("H");
if ($t < "22"){
	echo " I am going to sleep";
}
?>

Output "I watch TV" if the current time is less than 20, and "I play a game" otherwise:

<?php
$t = date("H");
if ($t < "18") {
	echo "I watch TV";
} else {
	echo "I play a game";
}
?>

A variable starts with the $ sign, followed by the name of the variable A variable name must start with a letter or the underscore character A variable name cannot start with a number A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ) Variable names are case-sensitive ($age and $AGE are two different variables)

- A variable starts with the $ sign, followed by the name of the variable - A variable name must start with a letter or the underscore character - A variable name cannot start with a number - A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ) - Variable names are case-sensitive ($my_car, $mycar, $myCar, $MYCAR, $MYcar are four different variables)

 
// Correct Syntax  ($variable_name = "Value";)
    $my_car = "BMW";
   
// Incorect Syntax
    my_car = "BMW";
    $7my_car = "BMW";
    $my&car = "BMW";

PHP's most used variable scopes are: - local - global A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:

<?php
   $name = "Tornike";  // global scope
   function greeting() {
     echo "Hello " . $name . "!"; // using $name will generate an error
   } 
   greeting();

   echo "Hello" . $name . "!"; // using $name will generate output (Hello Tornike!)
?>

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:

<?php
   function greeting() {
     $name = "Tornike";  // local scope
     echo "Hello " . $name . "!";  // using $name inside the function will generate output (Hello Tornike!)
   } 
   greeting();

   echo "Hello" . $name . "!"; // using $name outside the function will generate an error
?>

The global keyword is used to access a global variable from within a function. To do this, use the global keyword before the variables (inside the function):

<?php
  $x = 70;
  $y = 7;

  function myNum {
    global $x, $y;
    $y = $x + $y;
  }
  
  myNum();
  echo $y; // output is 77
?>

HP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.

<?php
  $x = 70;
  $y = 7;

  function myNum {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
  }
  
  myNum();
  echo $y; // output is 77
?>

Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job. To do this, use the static keyword when you first declare the variable:

<?php
function myTest() {
  static $x = 0;
  echo $x;
  $x++;
}

myTest(); // output  is 1
myTest(); // output  is 2
myTest(); // output is 3
?>

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called. Note: The variable is still local to the function.

Constants are similar to variables except that they cannot be changed or undefined after they've been defined. Begin the name of your constant with a letter or an underscore. To create a constant, use the define() function:

define(name, value, case-insensitive)

Parameters: name: Specifies the name of the constant; value: Specifies the value of the constant; case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false; The example below creates a constant with a case-sensitive name:

<?php
  define("georgian_player", "Kvicha Kvaratskhelia");
  echo georgian_player;
  // Outputs "Kvicha Kvaratskhelia"
?>

The example below creates a constant with a case-insensitive name:

<?php
  define("georgian_player", "Kvicha Kvaratskhelia", true);
  echo Georgian_Player;
  // Outputs "Kvicha Kvaratskhelia"
?>

No dollar sign ($) is necessary before the constant name.