How can I add outside code in codeigniter?

It's possible to put use your existing code as a library in CodeIgniter. A library in CI is basically a class with one or more methods (functions) inside it.
You library goes into the application/libraries folder, and the file name must begin with a capital letter. E.g. Mylibrary.php

In order to use the library, load it from your controller:

PHP Code:

$this->load->library('mylibrary'); 


If your library contains a method named "display_page", call it like this:

PHP Code:

$this->mylibrary->display_page(); 


If your existing code is not in a class, but in procedural style, you can use it as a helper in CodeIgniter. Put the code in a file in the application/helpers folder. In order to access the functions inside the helper, call it like this:

PHP Code:

$this->load->helper('helperfile'); 


Now, the functions are available.