For while and do while

Question

Hi everybody, I'm a newbie and I have 2 questions about loops.
1) I've read somewhere that I can always switch from "for" to "while" and back, but what about "do while"? Are there any cases where you can do something only using do while?
2) In a for loop, if I change i++ to ++i can I see some differences? Do I need to modify my code sonewhere or may I have different results because if this?
Tnx for your help

Answer 1

Ok it is much more clear now. Thanks everybody!