Programmatically set default billing/shipping address of customers if they are not set in magento

magento-set-defaults-address.php

<?php

require_once ("app/Mage.php");
umask(0);
Mage::app("default");


$collection = Mage::getModel('customer/customer')->getCollection()->addAttributeToSelect('*');

foreach ($collection as $customer) {
	
	$customerObj = Mage::getModel('customer/customer')->load( $customer->getId() );
	
	if ( ! $customerObj->getDefaultBillingAddress() ) {
		foreach ($customerObj->getAddresses() as $address) {
			$address->setIsDefaultBilling(true);
			continue; // we only want to set first address of the customer as default billing address
		}
	}

	if ( ! $customerObj->getDefaultShippingAddress() ) {
		foreach ($customerObj->getAddresses() as $address) {
			$address->setIsDefaultShipping(true);
			continue; // we only want to set first address of the customer as default shipping address
		}
	}
}

How dynamically to switch on/off default billing and shipping address on customer side based on dynamic_shipping/dynamic_billing parameter?

I am using Magento 1.9.2.4. What change do I need to make in magento/app/code/core/Mage/Customer/controllers/AddressController.php in formPostAction() in case when $address->getIsDefaultBilling() or $address->getIsDefaultShipping() are 0, to unset the defaultBilling Address or defaultShipping Address values to null, because I don't want to show their defaults representatives on frontend:
http://magento.com/index.php/customer/address/index/

We should use break instead of continue in above foreach to set first one as default and definitely save it.

The problem with this implementation is that it can get any address, be it shipping or billing so long as it is first on the list and assign it as the default shipping address. The correct way is to browse through all the addresses and select the first shipping address put the if within your foreach that will check if the address is a billing address then afterwards break out of the foreach🙏