php基础：递归求和函数

/*//递归
function sum($n){
    if($n>1){
        return $n+sum($n-1);
    }else{
        return 1;
    }
}

echo sum(-100); //返回5050
//递归求和函数
/*sun(5) = 5+sum(4);
sum(4) = 4+sum(3);
sum(3) = 3+sum(2);
sum(2) = 2+1;*/
/*拿到题目先列已知条件 会写的先写出来 不会的再找规律*/

//用递归的方式打印出当前目录及子目录
function showDir($path,$level = 0){
    $fh = opendir($path);
    while(($row = readdir($fh)) !== false){
        if(($row == '.')||($row == '..')){
            continue;
    }
        $row = mb_convert_encoding($row,'utf-8', "gbk");//输出转换为GBK编码
        echo str_repeat("&nbsp;&nbsp;&nbsp;&nbsp;",$level),$row,'<br/>';
        if(is_dir($row)){
            showDir($path.'/'.$row,$level+1);
        }
    }
    closeDir($fh);
}
  showDir('.');