My question is mostly about pure rules and not about etiquette. I wonder if during a chess game I am allowed to resign, offer a draw or claim a draw at any time. But I want to ask about two specific situations.
My opponent has just put my king in check. It is not a checkmate though. According to the rules of chess, instead of making a move, do I have the possibility of resigning, offering or claiming a draw? (If I do so, my king will remain in check in final position, but the game will end.)
The game is still in its opening. Suppose my opponent, who is a very strong player, put me in the situation where checkmate is inevitable, for example, he/she captured my queen and both rooks, or activated Légal trap etc. May I resign (it's the opening)? Or must I let my opponent checkmate me?