How to add Search box in Header in Wordpress

//Just put this code in header file where you want to display search box

<form method="get" id="searchform" action="<?php bloginfo('home'); ?>/">
<div><input type="text" size="25" value="<?php echo wp_specialchars($s, 1); ?>" name="phpcluster" id="phpcluster" />
<input type="submit" id="searchsubmit" value="Search" class="php cluster" />
</div>
</form>