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<?php
$a = 10;
$b = 3;

echo $a + $b;   // 13  Addition
echo $a - $b;   // 7   Subtraction
echo $a * $b;   // 30  Multiplication
echo $a / $b;   // 3.333...  Division (note: PHP division always returns a float)
echo $a % $b;   // 1   Modulus (remainder)
echo $a ** $b;  // 1000  Exponentiation (PHP 5.6+, 10 to the power of 3)

// Negation
echo -$a;       // -10  Negation
?>

<?php
$x = 10;

$x += 5;   // $x = $x + 5;   → 15
$x -= 3;   // $x = $x - 3;   → 12
$x *= 2;   // $x = $x * 2;   → 24
$x /= 4;   // $x = $x / 4;   → 6
$x %= 4;   // $x = $x % 4;   → 2
$x .= " yuan"; // $x = $x . " yuan"; → "2 yuan" (string append assignment)
?>

<?php
$a = 5;
$b = "5";

// Loose comparison (== compares value only, auto-converts types)
var_dump($a == $b);    // bool(true)  — 5 equals "5"
var_dump($a != $b);    // bool(false)

// Strict comparison (=== compares both value and type)
var_dump($a === $b);   // bool(false) — 5 doesn't equal "5" (different types)
var_dump($a !== $b);   // bool(true)

// Greater / less than
var_dump($a > 3);      // bool(true)
var_dump($a >= 5);     // bool(true)
var_dump($a < 10);     // bool(true)
var_dump($a <= 5);     // bool(true)

// Spaceship operator (PHP 7+) <=>
// Returns -1 if left is smaller, 0 if equal, 1 if left is larger
echo 1 <=> 2;   // -1
echo 2 <=> 2;   // 0
echo 3 <=> 2;   // 1
// Commonly used in sorting callbacks
?>

<?php
// In a search engine, a user might enter "0"
$search = "0";

// ❌ Wrong approach
if ($search == false) {
    echo "You didn't enter a search term"; // This runs! Because "0" == false
}

// ✅ Correct approach
if ($search === "") {
    echo "You didn't enter a search term"; // "0" !== "", won't misjudge
}
?>

<?php
$age = 20;
$hasTicket = true;

// AND (both must be true)
var_dump($age >= 18 && $hasTicket);   // bool(true)
var_dump($age >= 18 and $hasTicket);  // bool(true) — lower precedence than &&

// OR (at least one must be true)
var_dump($age < 18 || $hasTicket);    // bool(true) — has a ticket, so can enter
var_dump($age < 18 or $hasTicket);    // bool(true) — lower precedence than ||

// NOT (negation)
var_dump(!$hasTicket);  // bool(false)
var_dump(!false);       // bool(true)

// XOR (true when the two are different)
var_dump(true xor false);  // bool(true)
var_dump(true xor true);   // bool(false)
?>

<?php
$name = "John";
echo "Hello, " . $name . "!";  // Hello, John!

$html = "<div>";
$html .= "<h1>Title</h1>";
$html .= "<p>Content</p>";
$html .= "</div>";
echo $html;
// <div><h1>Title</h1><p>Content</p></div>
?>

<?php
$age = 20;

// Format: condition ? value_if_true : value_if_false
$status = ($age >= 18) ? "Adult" : "Minor";
echo $status;  // Adult

// The above is equivalent to:
if ($age >= 18) {
    $status = "Adult";
} else {
    $status = "Minor";
}

// PHP 5.3+ shorthand (omit the middle part)
$username = $_GET['name'] ?: "Guest";
// Equivalent to: use $_GET['name'] if it's truthy, otherwise "Guest"
?>

<?php
// ?? operator: use the left side if it's not null, otherwise use the right side
$username = $_GET['user'] ?? "Anonymous";
// Equivalent to: isset($_GET['user']) ? $_GET['user'] : "Anonymous"

// ??= operator (PHP 7.4+): assign only if the left side is null
$config = null;
$config ??= "default";   // $config is now "default"

$config2 = "existing value";
$config2 ??= "default";  // $config2 is still "existing value" (not null, so no overwrite)

// The difference between ?? and ?: 
$name = "";
echo $name ?: "default";   // "default" (empty string is falsy)
echo $name ?? "default";   // "" (empty string is not null)
?>

<?php
// Don't memorize the table — use parentheses to clarify intent
$result = $a + $b * $c;        // Unclear
$result = $a + ($b * $c);      // Clear

// Same for complex conditions
if (($age >= 18 && $hasTicket) || $isVip) {
    echo "Entry allowed";
}
?>