//
     //
     //
     //
     //$x = "a"; //$a = "123"; //--echo $$x; //$x = "a"; //$a = "123"; //echo $$x; //echo 123; //$x="a"; //$a=123; //echo $$x; $x = "1"; $y = 1; echo gettype($x); //换行 echo "
"; echo gettype($y); echo "
"; //看返回值是什么类型，此处为布尔型； echo gettype(is_string($x)); echo "
"; //ture unset($y); //直接输出false； var_dump(isset($y)); //转类型使用：settype echo "
"; //敲黑板 $a = ""; $b = null; var_dump(isset($a)); var_dump(empty($a)); echo "
"; var_dump(isset($b)); var_dump(empty($b)); //点变成箭头了 $time = new DateTime(); $time->getTimestamp(); $arr = [1,2,3]; $arr2 = [ "name"=>1, 1=>2, 2=>3 ]; array_push($arr,4); array_pop($arr); count($arr); for ($i=0;$i
    
      $value){}