Adds a new user account and sends a new user email after registering for an event. Requires EE3 and its WP user integration add-on.

espresso_create_wp_user.php

<?php
add_action('action_hook_espresso_save_attendee_data','espresso_create_wp_user', 10, 1);
function espresso_create_wp_user($attendee_data) {
    if( email_exists( $attendee_data['email'] ) == NULL ) {
		global $org_options;	
		
		// Generate the password and create the user
		$password = wp_generate_password( 12, false );
		$user_id = wp_create_user( $attendee_data['email'], $password, $attendee_data['email'] );
	
		// Set the users details
		//Additional fields can be found here: http://codex.wordpress.org/Function_Reference/wp_update_user
		wp_update_user(
			array(
				'ID'			=> $user_id,
				'nickname'		=> $attendee_data['fname'] . ' ' . $attendee_data['lname'],
				'display_name'	=> $attendee_data['fname'] . ' ' . $attendee_data['lname'],
				'first_name'	=> $attendee_data['fname'],
				'last_name'		=> $attendee_data['lname'],
				'description'	=> __('Registered via event registration form.', 'event_espresso'),
			)
		);
	
		// Set the role
		$user = new WP_User( $user_id );
		$user->set_role( 'subscriber' );
	
		// Get the username
		$user_info = get_userdata( $user_id );
		$user_name = $user_info->user_login;
	
		// Email the user
		wp_mail( $attendee_data['email'], 'Welcome to ' . $org_options['organization'], 
			'Your Username: ' . $user_name . ' Your Password: ' . $password . 
			' You can log in and view your registrations by clicking this link: ' 
			. wp_login_url( admin_url( 'users.php?page=my-events' ) ) );

		// add this user account to the event they just registered for
		if (defined('EVENTS_MEMBER_REL_TABLE')) {
			require_once(EVENT_ESPRESSO_MEMBERS_DIR . "member_functions.php"); //Load Members functions
			require(EVENT_ESPRESSO_MEMBERS_DIR . "user_vars.php"); //Load Members functions
			if ($user_id != 0) {
				event_espresso_add_user_to_event( $attendee_data['event_id'], $user_id, $attendee_data['attendee_id'] );
			}
		}
	
	} // end if

}