<!DOCTYPE HTML>
<html>
<!-- here there is a php code executed by the server, client receive only the output -->
<?php 
// We use a file to store the counter
// THE FOLLOWING CODE IS NOT SAFE! Multiple instance of the web server can 
// conflict on writing file; we use this code only for educational purposes. 
//
$file='/tmp/countx.txt';

//read counter
if(file_exists($file)) {
	$handle = fopen($file, "r");
	$x=(int)fread($handle,100);
	fclose($handle);
}else{
	$x=0;
}

if ($_GET['reset']){
	//reset counter
	$x=0;
}else{
	//increase counter
	$x=$x+1;
}

//write back the counter
$handle = fopen($file, "w");
fwrite($handle,"".$x);
fclose($handle);
?>

<!-- end of the php code -->
<body>
Visit Count:
<!-- here there is a php code executed by the server, client receive only the output -->
<?php
//out the counter
echo $x;
?>
<!-- end of php code -->
<br>
<a href="visit_count.php">reload</a>
<a href="visit_count.php?reset=yes">reset</a>
<br /><i>Watch the client-side HTML code and compare with the <a href="visit_count_code.php">server-side code</a></i>
</body>
</html>
The code of visit_count.php
