Hello Rozali, They both could be used interchangeably in many cases to give permission in a polite way for example: "Can I use your cellphone ?" "Of course, you can." or "Sure, you can." You can use both. 'Of course' means it is a normal thing ,it goes without saying .It emphasizes someone's agreement "of course" or disagreement " of course not". 'Sure' means it is definite, certain and free from doubt. It emphasizes that something (using the phone here) is reliable. It is also many times just an informal way of saying 'yes' or 'all right' .

A course is a pathway or direction. So you can understand "of course" to mean "that is they way it naturally goes" (not literally, just the idea of following a course). To be "sure" means to be definite, secure. As a phrase it works to assure the other person that you think things are correct, agreeable and true. You can use them interchangeably, it's really a matter of taste which you choose.

You can also say, "absolutely" or "I agree"

When they are used as responses, they mean the same thing. However, "of course" is more like 當然，and "sure" is more like ”好“.

Also, "of course" can be used as an exclamation such as "Of course it happened that way!" ... where as "sure" would not work in such a case...