Header and page redirection

[sridharao]

On the top of page, even before html tags are open, I have placed script to check for sessions. Later in the page according to the user submitted options, user is redirected to different pages using header.

switch($rsl){
    case "A":
        header("location: pagea.php");
        break;
    case "B":
        header("location: pageb.php?");
        break;
    case "C":
        header("location: pagec.php?");
        break;
    default:
        header("location: paged.php?");
} 

This works perfect in wampserver on my system. But on the web server, I get an error that header has already been sent.

Should I include this code on top of the page, but remember the page direction should occur only after user makes some selections.