PHP visitor counter

<?php
//               PHP访客计数器
function num()
{
 if(!file_exists("n.txt"))
 {
  $fp=fopen("n.txt","w");
  fwrite($fp,"1");
  fclose($fp);
  $n=1;
 }
 else
 {
  $fp=fopen("n.txt","r");
  $n=fgets($fp);
  fclose($fp);
  $n++;
  $fp=fopen("n.txt","w");
  fwrite($fp,$n);
  fclose($fp);
 }
 return $n;
}
?>

When using this program, you need to upload it to the corresponding directory, and then add the following code to the page that displays the number of visitors:
require_once"count.php";
$guestsnum=num();
echo"You are the ".$guestsnum. "Visitor";