You cant do that without a nasty hack.
What you should do is perform all your logic BEFORE you output html. A simple example follows:
<?php
//index.php
//perform logic and set variables before any html
$page = isset($_GET['menu'])?$_GET['menu']:'home';
switch($page){
case 'home':
$title = ' welcome to myco.ltd';
$content = 'pages/home.php';
break;
case 'about':
$title = 'about us';
$content = 'pages/about.php';
break;
case 'contact':
$title = 'get in touch';
$content = 'pages/contact.php';
break;
}
//the following html could be in a separate file and included, eg layout.php
?>
<html>
<head>
<title><?php echo $title;?></title>
</head>
<body>
<!--menu and other shared html here-->
<?php include $content;?>
<!-- shared footer stuff here-->
</body>
</html>
This is essentially a VERY barebones router script, an essential component of any framework. I would highly recommend you consider a lightweight framework rather than write everything from scratch. http://fatfreeframework.com/home would be a great start