Use the site_url() function inside the menu view.
<?php
defined('BASEPATH') OR exit('No direct script access allowed');
?>
<div id="menu">
    <ul>
        <li>
            <a href="<?php echo site_url('welcome');?>">Home</a>
        </li>
        <li>
            <a href="<?php echo site_url('welcome/catalog');?>">Catalog</a>
        </li>
        <li>
            <a href="<?php echo site_url('welcome/tickets');?>">Tickets</a>
        </li>
        <li>
            <a href="<?php echo site_url('welcome/log-in');?>">Log In</a>
        </li>
        <li>
            <a href="<?php echo site_url('welcome/About');?>">About</a>
        </li>
    </ul>
</div>
<?php
defined('BASEPATH') OR exit('No direct script access allowed');
?>
<div id="menu">
    <ul>
        <li>
            <a href="./">Home</a>
        </li>
        <li>
            <a href="./catalog">Catalog</a>
        </li>
        <li>
            <a href="./tickets">Tickets</a>
        </li>
        <li>
            <a href="./log_in">Log In</a>
        </li>
        <li>
            <a href="./about">About</a>
        </li>
    </ul>
</div>