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Valeri Tandilashvili's PHP Notes
Results: 135
PHP else-if statement CODE
The code will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday, otherwise it will output "Have a nice day!" 
$d = date("D");
if($d == "Fri"){
    echo "Have a nice weekend!";
} elseif($d == "Sun"){
    echo "Have a nice Sunday!";
} else{
    echo "Have a nice day!";
}
echo "\n";
Outputs 
Have a good morning!
if the current time is less than 10, and 
Have a good day!
if the current time is less than 20. Otherwise it will output 
Have a good night!
$t = date("H");
if ($t < "10") {
	echo "Have a good morning!";
} elseif ($t < "20") {
	echo "Have a good day!";
} else {
	echo "Have a good night!";
}
Prints 
Adult
If 
$age
is more than 
18
, and 
Teenager
if the variable is less than 12. Otherwise it prints 
Child
$age = 20;
if ($age > 18) {
    echo 'Adult';
} else if ($age > 12) {
    echo 'Teenager';
} else {
    echo 'Child';
}
PHP If statement CODE
If the current day is Friday the code will output "Have a nice weekend!" PHP datetime format: https://www.php.net/manual/en/datetime.format.php 
$d = date("D");
if ($d == "Fri"){
    echo "Have a nice weekend!";
}
If the current hour is less than 20, the code will output "Have a good day!" 
$t = date("H");
if ($t < "20") {
  echo "Have a good day!";
}
If 
$age
is more than 
18
, prints 
Adult
$age = 20;
if ($age > 18) {
	echo 'Adult';	
}
Array types CODE
Indexed array 
$colors = ["Red", "Green", "Blue"];
$colors[] = "Yellow";
Associative arrays 
$student = [
	"name"=>"George", 
	"weight"=>77, 
	"height"=>1.8, 
	"male"=>true
];
$student["male"] = true;
echo 'George is ' . $student['weight'] . 'kg'."\n";
Multidimensional arrays 
$students = [
	"George"=> [
		"name"=>"George", 
		"weight"=>77, 
		"height"=>1.8, 
		"male"=>true
	],
	"Alex"=> [
		"name"=>"Alex", 
		"weight"=>87, 
		"height"=>2.8, 
		"male"=>true,
		"parents"=> [
			"father"=>"David",
			"mother"=>"Marta",
		]
	],
	
];
echo 'Alex weighs ' . $students['Alex']['weight'] . 'kg'."\n";
echo "Alex's father is: " . $students['Alex']['parents']['father'];
Math functions CODE
Function 
min()
finds the lowest value from its arguments 
echo min(10, 15, 7, 9, 17)."\n"; // 7
Function 
max()
finds the highest value from its arguments 
echo max(10, 15, 7, 9, 17)."\n"; // 17
Function 
count()
counts all elements in the array 
echo count([10, 15, 7, 9, 17])."\n";
Function 
round()
rounds a floating-point number to its nearest integer 
echo(round(0.75))."\n";  // returns 1
echo(round(0.5))."\n";  // returns 1
echo(round(0.49))."\n";  // returns 0
Function 
floor()
rounds the floating-point number down 
echo floor(3.3)."\n";// 3  
echo floor(7.84)."\n";// 7 
echo floor(-4.8)."\n";// -5
Function 
ceil()
rounds the floating-point number up 
echo ceil(3.3)."\n";// 4
echo ceil(7.84)."\n";// 8
echo ceil(-4.8)."\n";// -4
Function 
rand()
generates a random number 
echo rand()."\n";
// Generates a random number from the range
echo rand(10, 100)."\n";
Function 
sqrt()
returns the square root of a number 
echo sqrt(64)."\n";  // 8
Function 
pow()
raises 2 to the power of 3 
echo pow(2, 3)."\n";  // 8
Function 
pi()
Returns PI value 
echo pi()."\n";// 3.1415926535898
Function 
abs()
returns the positive (absolute) value of a number 
echo abs(-12)."\n";
Function 
decbin()
converts decimal number into binary 
echo decbin(2)."\n";// 10
Differences between echo and print CODE
1. 
echo
can take multiple parameters 
echo 'one', 'two', 'three', "\n";
2. 
print
statement returns 1 
$print_returns = print('some text')."\n";
echo "print_returns Value: $print_returns" . "\n";
echo
prints 1 after 
print
statement is executed 
echo print "123", "\n";
3. 
echo
is a little bit faster than 
print
Recursive function for multi level tree view selector
The function gets data table, passes to recursive function to get associative array back. Encodes the array to JSON and returns back to user:
public function getCategoryTreeJSON()
{
    $query = "  SELECT
                    c1.id,
                    c1.name,
                    c1.parent_id,
                    (
                        SELECT
                            COUNT(c2.id) 
                        FROM
                            categories AS c2 
                        WHERE
                            c2.parent_id = c1.id
                    )
                    AS children_count 
                FROM
                    categories AS c1";

    $categoryDetails = json_decode(json_encode(DB::select($query)), true);
    
    $array_tree = $this->getCategoryTreeArray($categoryDetails);

    return json_encode($array_tree);
}
Recursive function that returns multi level associative array. Base case: when 
children_count
is equal to zero.
public function getCategoryTreeArray($items, $parent_id = 0)
{
    $branch = [];
    $array_JSON = [];  

    foreach ($items as $item) {
        if ($item['parent_id'] == $parent_id) {

            if ($item['children_count'] > 0) {
                
                $array_JSON[] = [
                    'id'=>$item['id'],
                    'title'=>$item['name'],
                    'subs'=>$this->getCategoryTreeArray($items, $item['id'])
                ];
                
            } else {
                
                $array_JSON[] = [
                    'id'=>$item['id'],
                    'title'=>$item['name']
                ];
            }
            
        }
    }
    return $array_JSON;
}
method() -> chaining() 
class Say {
    public function let() {
        echo 'Let' . " ";
        return $this;
    }
    public function me() {
        echo 'Me' . " ";
        return $this;
    }
    public function tell() {
        echo 'Tell' . " ";
        return $this;
    }
    public function you() {
        echo 'You' . " ";
        return $this;
    }
    public function something() {
        echo 'Something' . " ";
    }
}
$phrase = new Say;
$phrase->let()->me()->tell()->you()->something();
__get & __set 
__get
and 
__set
methods are called when there is an attempt either to use or to set a new value to any of the class property
class Person{
    public $firstName;
 
    public function __get($propertyName){
        echo "attempted to read property: $propertyName" . PHP_EOL;
    } 
    public function __set($propertyNane, $propertyValue){
        echo "attempted to set new value to property: $propertyNane" . PHP_EOL;
    } 
}
 
$p = new Person();
 
$p->firstName = 'Doe';
echo $p->firstName . PHP_EOL;
 
$p->lastName = 'John';
echo $p->lastName;
If the property is 
public
, the methods are not going to be called (if the property does not exist, or exists but is not public, the methods will get called) If we make 
$firstName
property 
private
or 
protected
, the methods will be called for the 
$firstName
property 
__get
, 
__set
, 
__call
and 
__callStatic
are invoked when the method or property is inaccessible
we can not use $this (object properties) inside static methods 
class Wheather {
    public $nonStatic = 0;
    public static $tempConditions = ['cold', 'mild', 'warm'];
    public static $someProperty = 5;

    static function celsiusToFarenheit($celsius) {
        return $celsius * 9 / 5 + 32 + $this->nonStatic;
    }
}

echo Wheather::celsiusToFarenheit(0);
echo "\n";
In this case we will get the error: 
Fatal error:  Uncaught Error: Using $this when not in object context
PHP For loop CODE 
if
has only one section: 
Condition
if (Condition) {
    // Code to be executed
}
for
loop has three sections divided by 
;
for (Initialization;   Condition;   Increment/Decrement) {
    // Code to be executed
}
The loop prints numbers from 0 to 10 
for ($i = 0;  $i < 10;  $i ++) {
	echo $i . "\n";
}
Results: 135