$number = 123;
echo $number;  // 输出 123

$maxInt = PHP_INT_MAX;
echo $maxInt;  // 输出 9223372036854775807

$pi = 3.14;
echo $pi;  // 输出 3.14

$bigNumber = 1.234567890123456789;
echo $bigNumber;  // 输出 1.2345678901235

$name = "John Doe";
echo "My name is {$name}.";  // 输出 My name is John Doe.

$length = strlen($name);
echo $length;  // 输出 8

$flag1 = true;
$flag2 = false;

if ($flag1) {
    echo "Flag 1 is true.";
} else {
    echo "Flag 1 is false.";
}

if ($flag2) {
    echo "Flag 2 is true.";
} else {
    echo "Flag 2 is false.";
}

$fruits = array("apple", "banana", "orange");
echo $fruits[0];  // 输出 apple

$person = array("name" => "John Doe", "age" => 20);
echo $person["name"];  // 输出 John Doe

class Circle {
    public radius;

    public function getArea() {
        return 3.14 *this->radius * this->radius;
    }
}circle = new Circle();
circle->radius = 5;
echocircle->getArea();  // 输出 78.5

$func = function () {
    echo "Hello world!";
};

$func();  // 输出 Hello world!

$numbers = [1, 2, 3, 4, 5];

foreach ($numbers as $number) {
    echo $number . " ";
}

// 输出 1 2 3 4 5

$var = null;

if (is_null($var)) {
    echo "Variable is null.";
} else {
    echo "Variable is not null.";
}