<?php

    //变量名可动态设置和使用
    //把一个变量的值作为另一个变量的名
    $a = "Hello";
    $$a = "World"; //相当于 $$a = ${$a} = $Hello
    $$$a = "www.hrkkid.com";

    echo $a;
    echo "<br>";
    echo $Hello;
    echo "<br>";
    echo $$a;
    echo "<br>";
    echo $World;

?>