PHP變量的作用域是什么？PHP變量的類型與檢測，分支結(jié)構(gòu)的實例

$name='張三';
echo $name;

$grade=5;
echo $grade;

$score=75.5;
echo $score;

$ispass=true;
var_dump($ispass); 

$subject=['語文','數(shù)學(xué)','英語'];
print_r($subject);

$actable = new stdClass();  // Object
$actable->name = '李四';
$actable->course = 'php';
$actable->grade = 80;
var_dump($actable);
var_dump($actable->course);
echo $actable->name, 

$link = fopen('hello.txt','r') or die('打開失敗');
echo fread($link, filesize('hello.txt'));
fclose($link);

$price = null;
echo '$price is ' . $price; echo is_null($price) ? '是NULL' : '不是NULL';

echo gettype($link);
echo gettype($actable);  

$age=15;

if($age<18){
    echo '你還未成年'; 
} 

$age=20;

if($age<18){
  echo '你還未成年'; 
}else{
   echo '你已成年'; 
} 

$age=27; 

if ($age < 18) {
    echo '你還未成年';
}elseif($age >= 18 && $age < 60) {    
    echo '你是輕中年';
}elseif($age>=60){
    echo '您是老年人'; 
}