Breakdown of Ich brauche ein Feuerzeug. Hast du eins?
ich
I
ein
a, an (eine)
du
you (informal singular)
haben
to have
Questions & Answers about Ich brauche ein Feuerzeug. Hast du eins?
Why is it eins at the end instead of just ein?
ein is an article (like a or an) and has to sit right next to a noun, like in ein Feuerzeug. But when you drop the noun entirely to just say one, you use a pronoun. For neuter nouns, that pronoun is eins.
Is eins in the accusative case here?
Yes! The verb haben (to have) always takes a direct object in the accusative case. For neuter words, the accusative pronoun eins happens to look exactly the same as the nominative (subject) form.
If I was asking about a masculine noun like der Stift (the pen), would I still use eins?
No, the pronoun has to match the gender and case of the noun it replaces. For a masculine noun in the accusative case, you would use einen. So you would ask: Hast du einen?
How would I answer No, I don't have one?
You would use the negative pronoun keins. You could say: Nein, ich habe keins. It works exactly the same way as eins but makes the sentence negative.