1-I will not be here for a whole week.
Can't this sentence mean two things:
a-I will be absent for a whole week.
b-I will be here for less than a week.
As always, context is everything. "Here" must refer to where the speaker is at the time of speaking so that should give the listener a clue.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.