Does every country have a constitution?

Does every country in the world (all 191 of them) have their own constitutions? That is, a formal document, a contract defining what the government is, what the people's rights are, what the government's duties & limitations are, etc.?

How does a country's government function if it has no constitution or founding document of any kind? (Not that it can't work -- the question is, how does everyone know how it's supposed to work when there are no blueprints to go by?)

Are copies of all the constitutions of all the countries in the world filed away at the United Nations? Or does the United Nations only keep records of copies of treaties between countries?

Speaking of which, a corollary question: Does every international organization (such as the United Nations, NATO, the European Union, etc.) have its own charter?

I also wonder what the difference is between a "constitution" and a "charter"... perhaps they're just two different words for the same thing.

Curious questions, these are!