How to overwrite cart controller add Action index Action in Magento

The Following Tutorial will Shows How to override cart controller Add Action or Index Action

First you need to give your Module name and Name_space ,I have taken Anjan as Namespace and override as Modulename
Now Create your module folders and files like below Instruction

1. Magento/app/code/local/Anjan/Override/etc/config.xml
2. Magento/app/code/local/Anjan/Override/controllers/CartController.php
3. Magento/app/etc/modules/Anjan_Override.xml

In config.xml Write the Foloowing code

<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
<Anjan_Override> <!--Change Anjan To Your Module NameSpace and Override to Your Module name-->
<version>0.1.0</version>
</Anjan_Override>
</modules>
<frontend>
<routers>
<checkout>
<args>
<modules>
<Anjan_Override before="Mage_Checkout">Anjan_Override</Anjan_Override><!--Change Anjan To Your Module NameSpace and Override to Your Module name-->
</modules>
</args>
</checkout>
</routers>
</frontend>
</config>

In CartController.php write the following code

<?php
require_once 'Mage/Checkout/controllers/CartController.php';
class Anjan_Override_CartController extends Mage_Checkout_CartController
{
public function addAction()
{
echo 'I successfully Override Cart Controller';
parent::addAction();
}
public function indexAction()
{
echo 'I successfully Override Cart Controller';
parent::addAction();
}
}
?>


In Anjan_Override.xml write the following code

<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
<Anjan_Override>
<active>true</active>
<codePool>local</codePool>
</Anjan_Override>
</modules>
</config>

Now upload these files into your server,refresh your cache , the click on Add to cart button you can see the message is displaying . You can use die() statement to make sure whether is overrides or not .