calender()

They're not in the right place in your controller (the index() method is not called when displaying the view you're getting the error message on), and you need to remove the surrounding PHP tags from the method calls when you put them in the controller (since the opening PHP tag is at the top of the controller).

You have a lot of questions posted in the forum regarding the same form. You can't solve the issues independently, and changes you make in solving one issue can make other issues appear or disappear. It's also fairly obvious that you need to go through the overview and tutorial sections in the manual (or go back through it, if you have already).

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide