用PHP怎么做树型目录

这是我写的《学校信息管理系统》的两层目录树，自己修改一下（纯PHP实现）：
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE>XX中学目录树</TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="leejd">
<META NAME="Keywords" CONTENT="动态、目录树、网络上多人操作">
<META NAME="Description" CONTENT="该脚本用于处理动态的目录树，为了便于网络上的多人操作，采用动态刷新">
<link rel="stylesheet" type="text/css" href="<?php require("phplib.php3"); $tree=readini(); echo $tree[0]; ?>"></HEAD><BODY bgcolor=#C0C8A8>
<?php //注意字段名分大小写
printf("<img border=\"0\" src=\"%s/dirminus.gif\">",$tree[2]);
printf("<a href=\"xs_xjgl_index_r.php3\" target=\"main\"><img border=\"0\" src=\"%s/open.gif\">XX中学</a><br>",$tree[2]);
$db=connectmysql();
if($id) //点击了某个班级
  {$result = mysql_query("SELECT * FROM jw_bj",$db);          
   while($myrowbj=mysql_fetch_array($result))  //该循环用于显示学校的各个班级
     {
      if($id==$myrowbj['BJBM_BJ'])
    {
 printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
 printf("<a href=\"%s\"><img border=\"0\" src=\"%s/dirminus.gif\"></a>",$PATH_INFO,$tree[2]);
 printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/open.gif\"></a>",$PATH_INFO,$myrowbj['BJBM_BJ'],$tree[2]);
 printf("<a href=\"%s?id=%s\" target=\"main\">%s</a><br>",'xs_bjjgl_index_r.php3',$myrowbj['BJBM_BJ'],bm2bj($myrowbj['BJBM_BJ']));
 $sql="select * from xs_xsxx where bjbm_xs='$myrowbj[0]' and xjzt_xs='正'"; 
 $resulta=mysql_query($sql,$db);
 $num=mysql_num_rows($resulta);
 $i=0;
         while($myrowxs=mysql_fetch_array($resulta)) //显示在校的该班级的学生
           {
    if($i==($num)-1) //最后一个
  {
   printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
   printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
   printf("<img border=\"0\" src=\"%s/lastblk.gif\">",$tree[2]);
   printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$myrowxs['XJH_XS'],$tree[2]);
       printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\">%s</a><br>",$myrowxs['XJH_XS'],$myrowxs['XM_XS']);
  }
else //非最后一个
  {
   printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
       printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
       printf("<img border=\"0\" src=\"%s/midblk.gif\">",$tree[2]);
   printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$myrowxs['XJH_XS'],$tree[2]);
       printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\">%s</a><br>",$myrowxs['XJH_XS'],$myrowxs['XM_XS']);
   $i++;
  }
   }
}
  else
    {
 printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
 printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/dirplus.gif\"></a>",$PATH_INFO,$myrowbj['BJBM_BJ'],$tree[2]);
 printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/close.gif\"></a>",$PATH_INFO,$myrowbj['BJBM_BJ'],$tree[2]);
 printf("<a href=\"%s?id=%s\" target=\"main\">%s</a><br>",'xs_bjjgl_index_r.php3',$myrowbj['BJBM_BJ'],bm2bj($myrowbj['BJBM_BJ']));
}
     }
   if($id=='其它')
    {
printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
printf("<a href=\"xs_treechld_r.php3\"><img border=\"0\" src=\"%s/lastminus.gif\"></a>",$tree[2]);
printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/open.gif\"></a>",$PATH_INFO,'其它',$tree[2]);
printf("<a href=\"%s?id=%s\">%s</a><br>",$PATH_INFO,'其它','其它'); //用于显示未在校的学生
$sqltx="select * from jg_jgxx where txbz_jg='退'";
        $resultb=mysql_query($sqltx,$db);
$numa=mysql_num_rows($resultb);
$j=0;
        while($myrowtx=mysql_fetch_array($resultb))
          {
   if($j==($numa-1))
     {
  printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
  printf("<img border=\"0\" src=\"%s/space.gif\">",$tree[2]);
      printf("<img border=\"0\" src=\"%s/lastblk.gif\">",$tree[2]);
  printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$myrowjg[0],$tree[2]);
      printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\">%s</a><br>",$myrowtx[0],$myrowtx[1]); //显示未在校的全校所有学生
 }
   else
     {
  printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
  printf("<img border=\"0\" src=\"%s/space.gif\">",$tree[2]);
      printf("<a href=\"xs_treechld_r.php3\"><img border=\"0\" src=\"%s/midblk.gif\"></a>",$tree[2]);
      printf("<a href=\"xs_treechld_r.php3\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$tree[2]);
      printf("<a href=\"xs_xsjgl_gk.php3?id=%s\" target=\"main\">%s</a><br>",$myrowtx[0],$myrowtx[1]); //显示未在校的全校所有学生
  $j++;
 }
  }
}
  else
    {
 printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
 printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/lastplus.gif\"></a>",$PATH_INFO,'其它',$tree[2]);
 printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/close.gif\"></a>",$PATH_INFO,'其它',$tree[2]);
 printf("<a href=\"%s?id=%s\">%s</a><br>",$PATH_INFO,'其它','其它'); //用于显示未在校的学生
}
   
   printf("<img border=\"0\" src=\"%s/lastblk.gif\"></a>",$tree[2]);
   printf("<a href=\"login.php3\" target=\"_parent\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$tree[2]);
   printf("<a href=\"%s\" target=\"_parent\">返回首页</a><br>",'login.php3'); //登陆首页的文件名 
  }
else //没有点击
  {
   $result = mysql_query("SELECT * FROM jw_bj",$db);          
   while($myrowbj=mysql_fetch_array($result))  //该循环用于显示学校的各个班级
     {
  printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
  printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/dirplus.gif\"></a>",'xs_treechld_r.php3',$myrowbj['BJBM_BJ'],$tree[2]);
  printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/close.gif\"></a>",$PATH_INFO,$myrowbj['BJBM_BJ'],$tree[2]);
      printf("<a href=\"%s?id=%s\" target=\"main\">%s</a><br>",'xs_bjjgl_index_r.php3',$myrowbj['BJBM_BJ'],bm2bj($myrowbj['BJBM_BJ']));
     }
   printf("<img border=\"0\" src=\"%s/line.gif\">",$tree[2]);
   printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/lastplus.gif\"></a>",$PATH_INFO,'其它',$tree[2]);
   printf("<a href=\"%s?id=%s\"><img border=\"0\" src=\"%s/close.gif\"></a>",$PATH_INFO,'其它',$tree[2]);
   printf("<a href=\"%s?id=%s\">%s</a><br>",$PATH_INFO,'其它','其它'); //未在校菜单   printf("<img border=\"0\" src=\"%s/lastblk.gif\"></a>",$tree[2]);
   printf("<a href=\"login.php3\" target=\"_parent\"><img border=\"0\" src=\"%s/txt.gif\"></a>",$tree[2]);
   printf("<a href=\"%s\" target=\"_parent\">返回首页</a><br>",'login.php3'); //登陆首页的文件名  
  }mysql_close($db);
?>
</BODY>
</HTML>