Rica ederim

I like your dry humor, Ahmet.

When SA is attached to the tense marking of a verb it denotes a real condition. When attached straight to the verb root it denotes an unreal condition.

For nouns and adjectives the rule goes like this: (Y)SA attached straight to the nominal root (or the negator değil) denotes a real condition. If you want to bring forth the meaning of an unreal condition you must call for the verb olmak for help and attach SA into its root. That is why you were corrected

                   Elbette mutluyuz. Mutlu değilsek olmasak böyle gülebilir miyiz

lana-.

To put it short and simple, an unreal condition is always of the form VERB ROOT + SA + WHATEVER...

teşekkürler Abla

Olmazsa gives sentence a future tense meaning. So your teacher is completely wrong. But dont say this to him if he is a prick

would you give an example gokuyum? 

Okula gitmezsem, babam kızar. If I dont go to school, my father will get angry.

There is sometimes a really thin line between tenses. Present tense can express a future event. "Okula gitmezsem(if I dont go to school)" maybe he is talking about tomorrow. He can still use present tense even if he is talking about it.

like in this sentence 

2 Yarın işten sonra yorgun olmazsam sinemaya gidelim

ty very much ^_^ I really had difficulties with this 

Yes lana. This is another example. Tenses are a little bit tricky in Turkish