I am getting this error when I tried to set up CodeIgnitor. 
Fatal error: Call to undefined function base_url() in
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C:\wamp\www\Test-CI\application\views\layout.php on line 5
 
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{main}( ) IN ..\index.php:0 require_once('C:\wamp\www\Test-CI\system\core\CodeIgniter.php' ) IN ..\index.php:202 
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call_user_func_array ( ) IN ..\CodeIgniter.php:359
 
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Home->index( ) IN ..\CodeIgniter.php:0
 
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CI_Loader->view( ) IN ..\home.php:17
 
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CI_Loader->_ci_load( ) IN ..\Loader.php:419
 
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include('C:\wamp\www\Test-CI\application\views\layout.php' ) IN ..\Loader.php:833 
My code :
 <html>
    <head>
        <meta http-equiv="Content-type" content="text/html; charset=utf-8">
        <title>Galleriffic | Custom layout with external controls</title>
        <link rel="stylesheet" href="<?php base_url(); ?>/assets/css/basic.css" type="text/css" />
        <link rel="stylesheet" href="<?php base_url(); ?>/assets/css/galleriffic-5.css" type="text/css" />
        
        <!-- <link rel="stylesheet" href="<?php base_url(); ?>/assets/css/white.css" type="text/css" /> -->
        <link rel="stylesheet" href="<?php base_url(); ?>/assets/css/black.css" type="text/css" />
        
        <script type="text/javascript" src="<?php base_url(); ?>/assets/js/jquery-1.3.2.js"></script>
        <script type="text/javascript" src="<?php base_url(); ?>/assets/js/jquery.history.js"></script>
        <script type="text/javascript" src="<?php base_url(); ?>/assets/js/jquery.galleriffic.js"></script>
        <script type="text/javascript" src="<?php base_url(); ?>/assets/js/jquery.opacityrollover.js"></script>
        <!-- We only want the thunbnails to display when javascript is disabled -->
        <script type="text/javascript">
            document.write('<style>.noscript { display: none; }</style>');
        </script>
    </head>
Can someone explain to me why this error occurred? and how can I solve this?