Problem: PHP Warning: Cannot modify header information – headers already sent by

I already saw that, and tried everything they said, but there isn’t any space before or after the <?php and ?>

I don’t know. I’m not an expert so I can’t read those things. Functions is like this:

<?php
if ( function_exists('register_sidebar') ) register_sidebar(array( 'name' => 'sidebar', 'before_widget' => '', 'after_widget' => '<br clear="all" /><br />', 'before_title' => '<div id="titulo-sidebar">', 'after_title' => '</div><br />', ));
register_sidebar(array( 'name' => 'blog', 'before_widget' => '', 'after_widget' => '<br clear="all" /><br />', 'before_title' => '<div id="titulo-sidebar">', 'after_title' => '</div><br />', ));
register_sidebar(array( 'name' => 'publicidade', 'before_widget' => '<div id="publicidade">', 'after_widget' => '</div>', 'before_title' => '', 'after_title' => '', ));

if ( function_exists( 'add_theme_support' ) ) :
add_theme_support( 'post-thumbnails' );
add_filter('widget_text', 'do_shortcode');

endif;

function post_pagination($pages = '', $range = 4)
{
     $showitems = ($range * 2)+1;  

     global $paged;
     if(empty($paged)) $paged = 1;

     if($pages == '')
     {
         global $wp_query;
         $pages = $wp_query->max_num_pages;
         if(!$pages)
         {
             $pages = 1;
         }
     }   

     if(1 != $pages)
     {
         echo "<div id='pagenavi'><font style='float:left; margin: 5px 10px 0 0;'>Página $paged de $pages</font>";
         if($paged > 2 && $paged > $range+1 && $showitems < $pages) echo "<a href='".get_pagenum_link($paged - 1)."' class='current'>Anterior</a>";
         if($paged > 4 && $showitems < $pages) echo "<a href='".get_pagenum_link(1)."'>1</a> <span class='current'>...</span>";

         for ($i=1; $i <= $pages; $i++)
         {
             if (1 != $pages &&( !($i >= $paged+$range+1 || $i <= $paged-$range-1) || $pages <= $showitems ))
             {
                 echo ($paged == $i)? "<span class='current'>".$i."</span>":"<a href='".get_pagenum_link($i)."' class='inactive' >".$i."</a>";
             }
         }

         if ($paged < $pages-1 &&  $paged+$range-1 < $pages && $showitems < $pages) echo "<span class='current'>...</span> <a href='".get_pagenum_link($pages)."'>$pages</a>";
         if ($paged < $pages && $showitems < $pages) echo "<a href='".get_pagenum_link($paged + 1)."' class='current'>Próxima</a>";
         echo "</div>\n";
     }
} 

if ( ! function_exists( 'parent_comment' ) ) :
function parent_comment( $comment, $args, $depth ) {
    $GLOBALS['comment'] = $comment;
    switch ( $comment->comment_type ) :
        case '' :
    ?>
        <li <?php comment_class(); ?> id="comment-<?php comment_ID() ?>"> <?php echo get_avatar( $comment, 74, $default = 'http://itcloset.com.br/wp-content/uploads/2014/07/avatar.png' ); ?>
<div class="comment">
<span class="commentname"> <b><?php comment_author_link(); ?></b><br>
<?php comment_date('j \d\e F \d\e Y') ?> às <?php comment_time('H:i'); ?> <?php edit_comment_link(' (Editar)','',''); ?>
</span>

            <?php comment_text() ?> 

            <?php if ( $comment->comment_approved == '0' ) : ?>
                <em class="comment-awaiting-moderation"><?php _e( 'Your comment is awaiting moderation.' ); ?></em>
            <?php endif; ?>  

            <?php comment_reply_link( array_merge( $args, array( 'depth' => $depth, 'max_depth' => $args['max_depth'] ) ) ); ?>     

</div>
        </li>  

<hr />

    <?php
            break;
        case 'pingback'  :
        case 'trackback' :
    ?>
    <li class="post pingback">
        <p><?php _e( 'Pingback:' ); ?> <?php comment_author_link(); ?><?php edit_comment_link( __( '(Edit)' ), ' ' ); ?></p>  

    <?php
            break;
    endswitch;
}
endif;
?>