Getting "undefined offset" and "invalid argument" errors - php

Question

I get these errors when I go the Reports.php page:
A PHP Error was encountered
Severity: Notice
Message: Undefined offset: 0
Filename: controllers/Reports.php
Line Number: 73
Backtrace:
File: C:\xampp\htdocs\restaurant\application\controllers\Reports.php
Line: 73
Function: _error_handler
File: C:\xampp\htdocs\restaurant\index.php
Line: 315
Function: require_once
A PHP Error was encountered
Severity: Warning
Message: Invalid argument supplied for foreach()
Filename: controllers/Reports.php
Line Number: 88
Backtrace:
File: C:\xampp\htdocs\restaurant\application\controllers\Reports.php
Line: 88
Function: _error_handler
File: C:\xampp\htdocs\restaurant\index.php
Line: 315
Function: require_once
This is line 73 in Reports.php:
$store_id = $store_data[0]['id'];
This is line 88 in Reports.php:
foreach ($order_data as $k => $v) {
This is line 315 in index.php:
require_once BASEPATH.'core/CodeIgniter.php';