conjunctions such as unless and if....not?

[spoon]

Dear teachers,

I want to ask you something related to conjuctions, especially unless and if..not.

Plz look at the following sentences.

a -I'll come back home OLOR="Red"]unless[/COLOR] there is a strike.
a'-I'll come back home if there is not a strike.

b-I'll be happy if you don't give it up.
b'-I'll be happy unless you give it up.

As far as I know, I think all the sentences except b' are right.

I'd like to know how and when to use those seemingly similar conjunctions.

Thanks in advance.

[dilekdemir89]

I think all of them are right, I can't see any option which cannot.