click submit button but cannot found page - codeigniter

Question

I want to make calculate the area of square, but when I click the submit button, page cannot be found :
controller :
<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Controller_luas extends CI_Controller {
public function coba_controller($panjang=0,$lebar=0){
$nilai['panjang_bangunan'] = $panjang;
$nilai['lebar_bangunan'] = $lebar;
$nilai['luas_bangunan'] = $this->mymodel->hitungluas($nilai);
$this->load->view('coba_view',$nilai);
}
}
view :
<form method="POST" action="<?php echo base_url()."index.php/controller_luas/"; ?>">
<table widht="200" border="1">
<tr>
<td>Panjang</td>
<td><input type="text" name="cari_judul"></td>
</tr>
<tr>
<td>Lebar</td>
<td><input type="text" name="cari_penulis"></td>
</tr>
<tr>
<td colspan="2"><input type="submit" value="Hasil"></td>
</tr>
</table>
<h1>Luas Perseginya yaitu : <?php echo $luas_bangunan ?><h1>
</form>
models :
function hitungluas($param=''){
$luas=$param['panjang_bangunan'] * $param['lebar_bangunan'];
return $luas;
}

Answer 1

When you are submitting to the controller Controller_luas
It is submitting to the index function even though I do not see it there.
If you need it to go to coba_controller function then in form action you need to add it.
With index.php
<form method="POST" action="<?php echo base_url('index.php/controller_luas/coba_controller'); ?>">
Without index.php
<form method="POST" action="<?php echo base_url('controller_luas/coba_controller'); ?>">
Using Codeigniter Form Helper
http://www.codeigniter.com/user_guide/helpers/form_helper.html
Or you can auto load this
$this->load->helper('form');
<?php echo form_open('controller_luas/coba_controller');?>
// Form Content
<?php echo form_close();?>
You also might be best to use codeigniter form validation library as well.