when we use Quanti and when we use Quanto?
I got confused.Does the nouns in Italian have countable and uncountable like English?

Question

Answer

Yes, italian has these two kinds of nouns.
You must say "Quanto zucchero vuoi?" because "zucchero" is uncountable. But you say "Quanti libri hai?"

Answer

Quanto/i = 多少
Quanto = 单数， 例如：这本书多少钱？ = Quanto costa questo libro?
Quanti = 复数，阳性， 例如： 多少书？ = Quanti libri?

拜拜

Answer

It's simple: Quanto with singular objects, Quanti with plural. 
They (almost) always correspond to the english How much (quanto) and How many (quanti).
And yes, in italian we do have something similar to uncountable nouns.

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