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 PHP date() function is used to format a date and/or a time. ➤ First of all, to get the right information, we need to set the default timezone:

date_default_timezone_set('Asia/Tbilisi');

• d - Represents the day of the month (01 to 31)

echo date("d"); // outputs:  current day of the month (01 to 31)

• D - A textual representation of a day (three letters)

echo date("D"); // outputs:  currnet day (three letters)

• m - Represents a month (01 to 12)

echo date("m"); // outputs:  current month (01 to 12)

• Y - Represents a year (in four digits)

echo date("Y"); // outputs:  current year (in four digits)

• l - Represents the day of the week

echo date("l"); // outputs:  current day (A full textual)

*

echo "Today is " . date("Y/m/d");  // outputs: Today is 2022/10/17
echo "Today is " . date("Y.m.d");  // outputs: Today is 2022.10.17
echo "Today is " . date("Y-m-d");  // outputs: Today is 2022-10-17
echo "Today is " . date("l");  // outputs: Today is Monday

• H - 24-hour format of an hour (00 to 23)

echo date("H"); // outputs:  current hour (00 to 23)

• h - 12-hour format of an hour with leading zeros (01 to 12)

echo date("h"); // outputs:  currnet hour (01 to 12)

• i - Minutes with leading zeros (00 to 59)

echo date("i"); // outputs:  current minutes (00 to 59)

• s - Seconds with leading zeros (00 to 59)

echo date("s"); // outputs:  current seconds (00 four 59)

• a - Lowercase Ante meridiem and Post meridiem (am or pm)

echo date("a"); // outputs:  current am/pm

- 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";

➤ In this note we will look at some commonly used math functions. •

pi()

// pi() function returns the value of PI:
echo pi(); // outputs 3.1415926535898

•

min()

•

max()

// min() and max() functions can be used to find the lowest or highest value in a list of arguments:
echo (min(1, 4, 35, -9, 48));  // outputs -9
echo (max(41, 12, 89, 23, -19));  // outputs 89

•

abs()

// abs() function returns the absolute (positive) value of a number:
echo abs(-4.5);  // outputs 4.5

•

sqrt()

// sqrt() function returns the square root of a number:
echo sqrt(81);  // outputs 9

•

round()

// round() function rounds a floating-point number to its nearest integer:
echo round(1.7); // outputs 2
echo round(1.3); // outputs 1

•

floor()

// floor() function rounds a number DOWN to the nearest integer:
echo floor(2.4); // outputs 2 
echo floor(3.8); // outputs 3 
echo floor(-1.1); // outputs -2

•

rand()

// rand() function generates a random number:
echo rand();
// Alo we can add the optional min and max parameters to specify the lowest integer 
// and the highest integer to be returned.
// For instance, random integer between 1 and 10 (inclusive), use rand(10, 100):
echo rand(1, 10);

•

count()

// count() function returns the number of elements in an array:
$countries = array("Georgia","Ukraine","Spain");
echo count($countries); // outputs 3

•

pow()

// pow() function returns x raised to the power of y. ( x = 2 , y = 3):
echo pow(2,3); // outputs 8

•

decbin()

// decbin() function converts decimal to binary:
echo decbin(2);// outputs 10
echo "\n";
echo decbin(10); // outputs 1010

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)

➤ In this note we will look at some commonly used functions to manipulate strings. •

strlen()

// function returns the length of a string.
echo strlen("Hello"); // outputs 5

•

str_word_count()

// function counts the number of words in a string.
echo str_word_count("Hello world!"); // outputs 2

•

strrev()

// function reverses a string.
echo strrev("Levani"); // outputs inaveL

•

strpos()

/* function searches for a specific text within a string. 
If a match is found, the function returns the character position of 
the first match. If no match is found, it will return FALSE.*/
echo strpos("Hello world!", "l"); // outputs 2 
// why ?     index 0 = "H", index 1 = "e" and index 2 = "l"

•

str_replace()

// function replaces some characters with some other characters in a string.
echo str_replace("l", "L", "levani"); // outputs Levani

•

substr()

// function return part of a string between given indexes
echo substr("Hello world", 6)."\n"; // outputs world
echo substr("Hello world", 9, 2)."\n"; // outputs ld
echo substr("abcdef", -1)."\n";    // outputs f
echo substr("abcdef", -2)."\n";    // outputs ef
echo substr("abcdef", -3, 1)."\n"; // outputs d

•

strtoupper()

// function  make a string uppercase
echo strtoupper("i love coding")."\n"; // outputs I LOVE CODING

•

strtolower()

// function make a string lowercase
echo strtolower("PHP")."\n"; // outputs php

•

explode()

// function Split a string by a string
echo var_dump(explode(" ", "I am 19 years old"))."\n"; // outputs "I" "am" "19" ...

•

implode()

// function  join array elements with a string
echo implode(" ", ['Nika', 'Giorgi',"Saba"]); // outputs Nika Giorgi Saba

•

trim()

// function strip whitespace (or other characters) from the beginning and end of a string
echo trim("              How are you ?     ")."\n";
// outputs How are you ? (without any whitespace before and after the text)

➤ 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

➤ 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";

➤ 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

• 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