➤ A comment in PHP code is a line that is not executed as a part of the program. Its only purpose is to be read by someone who is looking at the code. • Let others understand your code. • Remind yourself of what you did. PHP supports several ways of commenting:

// This is a single-line comment

# This is also a single-line comment

/*
This is a multiple-lines comment block
that spans over multiple
lines
*/

// You can also use comments to leave out parts of a code line
$a = 2 /* - 1 */ + 4;

➤ PHP

echo

statement can be used to print the string, multi-line strings, escaping characters, variable, array, etc. • printing string

echo "Hello friends!\n";

• printing multi line string

echo "How are you ?  
this is multi line  
text !\n";

• printing escaping characters

echo "Hello \"Hello\" Hello\n";

• printing variable value ( only DOUBLE quetes can parse variables )

$num= 17;  
echo "num = $num\n";  
// or => echo "num = ".$num."\n";
// or => echo 'num = '.$num."\n";

• printing number without quotes

echo 10;

• printing multiple parameters

echo "red"," yellow"," black";

• echo can be used with or without parentheses: echo(), and echo.

echo ("function\n");

• Text inside double quotes can include single quotes as part of the text. The opposite is also possible.

echo "My name is 'Anton'\n";
echo 'My name is "Anton"';

➤ PHP

print

statement works exactly the same way except that the print statement can only output one parameter, and always returns 1. • returns 1

$result = print"Hello\n";
echo "result = $result"; // output: 1

•

print

can take only one argument

print "hello","world"; // error

•

echo

statement considered marginally faster than the

print

statement since it doesn't return any value. •

print

always returns an integer value, which is 1.

$result = print 10;
echo $result; // output: 1

• Using

print

, we cannot pass multiple arguments.

print 10,20,30; // error

• String

$str = "string"; // "hello" "Gamarjoba" 'levani' and so on.

• Integer

$int_num = 10; // -12 400 9999 -123421 90 and so on.

• Float

$float_num = 2.5; // -1.5 20.5 150.7 and so on.

• Boolean

$human = true; // equals 1
$robot = false; // equals 0

• Array

$laptops = array("Dell","Lenovo","Hp",1,2,3);

• constant 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. (no $ sign before the constant name): • 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

define(name, value, case-insensitive)

// define constant
define("PI",3.141592);
echo PI;

I will discuss additional data types later, in a new note!

➤ In PHP, you can use the array() construct or [] syntax to define an array. • Indexed array — An array with a numeric key ( index ).

$arr = []; // or $arr = array();
$arr[0] = "Levani";
$arr[1] = "Nika";
$arr[2] = "Giorgi"; // or $arr = ["levani","Nika","Giorgi"]
$arr[] = "Saba"; // add last element in arr
echo "I am $arr[0] \n"; // output: I am Levani

• Associative array — An array where each key has its own specific value. In the following example the array uses keys instead of index numbers:

$ages = [
	"John" => 15,
	"Michael" => 25,
	"Levani" => 19,
	"Mads" => 57
	];
//          or
// $ages["John"] = "15";
// $ages["Michael"] = "25";
// $ages["Levani"] = "19";
// $ages["Mads"] = "57";
echo "I am ".$ages["Levani"]." years old \n"; // output: I am 19 years old

• Multidimensional array — An array containing one or more arrays within itself.

$laptop = [
	"Lenovo" => [
		"price" => 1200,
		"color" => "white",
		"storage" => "300 Gb",
		],
	"Dell" => [
		"price" => 1000,
		"color" => "black",
		"storage" => "500 Gb",
		],
	];
echo "My laptop price is ".$laptop["Dell"]["price"].".\n"; // output: My laptop price is 1000.

•

\n

represents the newline (linefeed)

echo "Co\nding\n";
// output:	    Co
//      	    ding

•

\t

represents the tab

echo "Co\tding\n";
// output:          Co	ding

• The increment operators are used to increment a variable's value. • The decrement operators are used to decrement a variable's value.

$x++; // equivalent to $x = $x+1;
$x--; // equivalent to $x = $x-1; 

• Increment and decrement operators either precede or follow a variable.

$x++; // post-increment 
$x--; // post-decrement 
++$x; // pre-increment 
--$x; // pre-decrement

• The difference is that the post-increment returns the original value before it changes the variable, while the pre-increment changes the variable first and then returns the value. For instance:

$a  = 2; $b = $a++; // $a=3,  $b=2
$a  = 2; $b = ++$a; // $a=3,  $b=3

$a  = 2; $b = $a--; // $a=1,  $b=2
$a  = 2; $b = --$a; // $a=1,  $b=1

➤ Assignment operators are used to write/uptade values to variables.

$x = 10;
$y = $x;
echo $y; // output: 10

Assignment	   Same as...	        Description
  $x = $y	  $x = $y	    The left operand gets set to the value of the expression on the right	
  $x += $y	  $x = $x + $y	    Addition	
  $x -= $y	  $x = $x - $y	    Subtraction	
  $x *= $y	  $x = $x * $y	    Multiplication	
  $x /= $y	  $x = $x / $y	    Division	
  $x %= $y	  $x = $x % $y      Modulus

For instance:

$x = 15;
$x %= 4; // output: 3
$x = 5;
$x *= 6; // output: 30

➤ Comparison operators compare two values (numbers or strings). Comparison operators are used inside conditional statements, and evaluate to either TRUE or FALSE.

Operator	 Name	                      Example	           Result	
  ==	        Equal	                     $x == $y	   Returns true if $x is equal to $y	
  ===	        Identical	             $x === $y	   Returns true if $x is equal to $y, and they are of the same type	
  !=	        Not equal	             $x != $y	   Returns true if $x is not equal to $y	
  <>	        Not equal	             $x <> $y	   Returns true if $x is not equal to $y	
  !==	        Not identical	             $x !== $y	   Returns true if $x is not equal to $y, or they are not of the same type	
  >	        Greater than	             $x > $y	   Returns true if $x is greater than $y	
  <	        Less than	             $x < $y	   Returns true if $x is less than $y	
  >=	        Greater than or equal to     $x >= $y	   Returns true if $x is greater than or equal to $y	
  <=	        Less than or equal to	     $x <= $y	   Returns true if $x is less than or equal to $y

For instance:

// Equal
$x = 50;  
$y = "50";

var_dump($x == $y); // returns TRUE because values are equal
echo "\n";

// Identical
$x = 50;  // integer type
$y = "50"; // string type

var_dump($x === $y); // returns false because types are not equal
echo "\n";

// Not equal
$x = 50;  
$y = "50";

var_dump($x != $y); // returns false because values are equal
echo "\n";

// Not equal. Both operators (!= / <>) give the same output. The only difference is that '<>' is in line with the ISO standard while '!= ' does not follow ISO standard.
$x = 50;  
$y = "50";

var_dump($x <> $y); // returns false because values are equal
echo "\n";

// Not identical
$x = 50;  
$y = "50";

var_dump($x !== $y); // returns true because types are not equal
echo "\n";

// Greater than
$x = 100;
$y = 50;

var_dump($x > $y); // returns true because $x is greater than $y
echo "\n";

// Less than
$x = 10;
$y = 50;

var_dump($x < $y); // returns true because $x is less than $y
echo "\n";

// Greater than or equal to
$x = 10;
$y = 10;

var_dump($x >= $y); // returns true because $x is greater than or equal to $y
echo "\n";

// Less than or equal to
$x = 10;
$y = 10;

var_dump($x <= $y); // returns true because $x is less than or equal to $y
echo "\n";

➤ PHP is partially case-sensitive. PHP constructs, function names, class names are case-insensitive, whereas variables are case-sensitive If we define a variable

$name = "Mads";

then we must need to use $name. $NAME will not work.

$name = "Mads";
echo $NAME; // output: error

If we defined function name in lowercase, but calling them in uppercase it will work. For instance, If we define function sum() {} then calling SUM() will also work.

function sum () {
	echo "10 + 10 = 20 \n";
}
SUM(); // output: 10 + 10 = 20