This is an old thread but I'd like to comment about the use of gonna.
Don't use it. "Gonna" is a colloquialism. All American children say it - we all say it occasionally, if truth be told. But, YOU shouldn't use it. Why? Because you want to sound educated so don't get into the lazy habit of saying "gonna" intead of "going to." Listen to this advice. People will think you are better educated if you don't use it. Also, even if you do use it occasionally do not ever write it!
Regarding "wanna," this is permissible for children only. Never use it. Never ever write it (horrors!)
Regarding could'a, would'a and should'a, as well as could of, would of and should of, all these expressions are perversions and should never be learned or spoken, not even once to prevent bad habits.
Use the following expressions only:
Going toHe's going to medical school. I'm going to the beach tomorrow. They're going home as soon as they get off work. Evelyn is going to swim tomorrow. I'm going to write a novel tomorrow.
I want to visit Brazil. I want to eat three pieces of cake.
Could have. I could have been a contender (what movie is this from?)
Should have. He should have followed his dreams instead of listening to his brother.
Could have. They could have lived happily ever after but life is tough on the waterfront. (hint)