源码高亮）PHP初作问题。求教。

<title>访问量计数器</title>  <?php  $n="0";  if(file_exists("num.txt"));  {  $fp=fopen("num.txt","r");  $n=fgets($fp,9);  $n++;  fclose($fp);  }  $fp=fopen("$fp","w");  fputs($fp,$n);  fclose($fp);  echo"<center><font color=red>Hello，这是第$n 次访问。</font></center>";  ?>  <?php  echo "<font color=green><br>时间：</font>";  ?>  <?php  echo date("Y年-m月-d日H时:m分:s秒");  ?>