function is_multi($array) {
    $filter = array_filter($array, 'is_array');
    print_r($filter);
    if(count($filter) > 0) {
    	return true;
    }
    return false;
}
var_dump(is_multi([
	"Valeri"=> [
		"weight"=>77, 
	],
	"Giorgi"=> [
		"weight"=>87, 
		"parents"=> [
			"father"=>"Daviti",
			"mother"=>"Mariami",
		]
	],
]));

function print_string(&$string) {
    $string = "Function string \n";
    echo($string);
}
$string = "Global string \n";
print_string($string);
echo($string);
// outputs: Function string, Global string

If we delete & (ampersand) symbol before variable, it outputs: Function string, Global string

$test = "Hello world";
echo str_replace("world", "Valer", $test);
// outputs: Hello Valer

strtr() simply translates the characters ONE BY ONE.

$test2 = "Hello world";
echo strtr($test2, "world", "Valer");
// outputs: Heeea Valer
// because it translated l > e, o > a. (w > V, r > l, d > r)

function arrayKeys($array) {
    print_r($array);
    return array_keys($array);
}
print_r(arrayKeys(["House" => "White", "Car" => "Black"]));

function arrayFillKeys($array) {
    print_r($array);
    $array = array_fill_keys($array, 'value');
    return ($array);
}
print_r(arrayFillKeys([4,3,2]));

$string = "hello world";
$pattern = "/world/";
echo preg_match($pattern, $string);
// outputs 1

therefore if that case would be like that:

$string = "Hello wORLD";
$pattern = "/world/i";
echo preg_match($pattern, $string);
// it would still outputs 1

For example: (via Regex - Regular Expression and preg_match)
(^[A-Z]*$) it means if there are only uppercase letters in a string.
(^[a-z]+$) it means if there are only lowercase letters in a string.
(^[A-Z]{1}[a-z]*$) it means if the first letter is uppercase in a string.
| - it means "Logical or" via regex as well.

 <?php
  function isPalindrome($s) {
        //s = "A man, a plan, a canal: Panama"
        $s= strtolower($s);
         $filtered = "";
        $len = strlen($s);
        for ($i= 0; $i<$len; $i++){
            $ascii = ord($s[$i]);
            if (($ascii>=97 && $ascii<123) ||
             ($ascii>47 && $ascii<58)){
                $filtered.=$s[$i];
                }
        }
        return $filtered == strrev($filtered);
    }
   $s = "A man, a plan, a canal: Panama";
   echo isPalindrome($s);

<?php
function space($sentence) {

$sentence= trim($sentence); //trim function-Breaks a sentence after spaces.

//str_contains-Checks if there is a blank in this sentence in this situation.
while (str_contains($sentence, '  ')) {

// str_replace-Replaces the first element with the second element in this sentence.
$sentence= str_replace('  ', ' ',$sentence);
}
return $sentence;
}
$sentence "  hi     i    am   gvanca";
echo space($sentence);

<?php 
function gettingmarried($women, $men) {

$count=count($women); //count-counts the number of women.

// '!=' -If not equal.
if ($women != count($men)) {
echo "I don't have all pairs";
}

//array_combine-Pairs the data of the first element with the second.
return  array_combine($women, $men);
}

print_r(gettingmarried(["elene","mariami"], ["dato", "vano"]));