一定会做的英文

这句话有点歧义啊，如果你要表达的是我一定会做到我说过的，可以说I will do as what I have said. 或者是 I will keep my promise. 但是如果你要表达的是 “我说过：我一定会做到”，那么应该用 I have said that I would make it.

be sure to do

I will achieve what I have said.

you must need sth.你一定需要什么东西 you must do sth.你一定要做什么事情