为什么计算器不计算了?!?!?!

<HTML>
<HEAD>
<TITLE>A PHP Example</TITLE>
</HEAD><BODY>
<?php
function jisu($coun_file)
{
$count=0;
if(file_exists($coun_file))
{
$fp=fopen($coun_file,"r");
$count=0+fgets($fp,20);
fclose($fp);
}
$count++;
$fp=fopen($coun_file,"w");
fputs($fp,$count);
fclose($fp);
return $count;
}
echo "你是第<font color=yellow>".jisu("count.txt")."</font>位访客";
?>
</BODY>
</HTML>大小写已区分了!