I've seen the following negative sentences in an English book. Placing a negative auxiliary before the first verb seems to be the right way:
I don't think she'll pass the exam.
The baby's tired. I don't think he's going to wake up tonight.
My question is, would it be grammatically acceptable to say:
I think she won't pass the exam. or
The baby's tired. I think he isn't going to wake up tonight.