How would one know the difference between "a cup of sugar" and "a sugar cup"?
Norwegian is like German, in that many words are compound words. "Sukkerkopp" means "sugar cup," and "kopp sukker" is "cup of sugar."
what if we don't know german...?
You'll be able to see it. It seems that if it's a compound word, it basically means the two words that went into it are the same thing: a sukkerkopp is a sugar-cup. But a kopp sukker is a cup (of) sugar.
so thers no "of" in norsk?