The simplest questions are those where one just answers with a yes or no. Such short answers are, by the way, acceptable in Croatian. In the Standard Croatian, the recipe for such simple questions is quite simple: move the verb to the beginning, if it isn't already there, and then insert a particle li² to the second position (before all other second-position words):
Ideš u školu. ▶ You're going to school.
Ideš li u školu? ▶ Are you going to the school?
— Da. Yes. / — Idem. I'm going.
— Ne. No. / — Ne idem. I'm not going.
If the verb in a sentence is present form of the verb biti be (that is, je², sam², etc.) the verb cannot be simply put to the beginning, since it must be in the second position!
Therefore, there are extended (or stressed) forms of the present of the verb biti, used when the verb must be the first word in a sentence. The forms are:
They are quite simple: just add je- to the beginning of usual forms, and you have the forms you need! Again, je² is an exception – it looks exactly the same in its normal and extended form. We can then ask:
Gladni ste. You're hungry. (to a group/someone you respect)
Jeste li gladni? Are you hungry?
— Da. Yes. / — Jesmo. We are.
— Ne. No. / — Nismo. We aren't.
As you can see, you can answer with either da or ne or with the verb in its extended form. There are no special extended negative forms, the usual negative forms of biti are already extended.
Now for the past tense. The past tense is made from two words, but for purpose of making questions, the auxiliary verb – the present tense of biti (je² +) be – is the important word. Grammatically, the past form behaves like a kind of adjective and has no role in making questions. Therefore, we need to move the auxiliary (je², sam², and so on):
Gledala si film. You watched the movie. (to a female)
Jesi li gledala film? ▶ Did you watch the movie?
— Da. Yes. / — Jesam. I did.
— Ne. No. / — Nisam. I didn't.
If je² is left out due to se², it must reappear in questions:
Bojao se. He was afraid.
Je li se bojao? Was he afraid?
Everything described so far was in the Standard Croatian. Colloquially, you will also hear and often read other ways of making such questions. The first one, and quite common, is to just put da li to the front, nothing else is changed, no verbs are moved, the present forms of biti don't get extended, etc:
Da li ideš u školu? ▶ (colloq.) Are you going to the school?
Da li ste gladni? ▶ (colloq.) Are you hungry?
Da li si gledala film? (colloq.) Did you watch the movie?
Da li se bojao? (colloq.) Was he afraid?
I used the abbreviation (colloq.) to remind you that these are colloquial sentences in Croatian®. It's very often seen and heard, e.g. on the wall in a (fancy) bakery:
This translates as Have you ever tasted a fresher sandwich? – the word kad, in yes/no questions, can mean ever as well (this will be explained in more detail in 41 Somewhere, Nobody, Everything...).
You will sometimes hear and read questions with these two words contracted to dal, or spelled together as dali.
Another option is to use the standard way, but without li:
Jesi gledala film? (colloq.) Did you watch the movie?
Yet another quite colloquial option is to put je li to the front, frequently contracted to just jel (also spelled as je l, je l'):
Jel ideš u školu? ▶ (colloq.) Are you going to the school?
Jel ste gladni? (colloq.) Are you hungry?
Jel si gledala film? (colloq.) Did you watch the movie?
Jel se bojao? (colloq.) Was he afraid?
Also, colloquially, it's possible to turn normal sentences into a question just by changing their intonation – sentences end on a higher tone, and are spoken faster – no rearrangement of any kind is needed:
Ideš u školu? ▶ (colloq.)
Gledala si film? (colloq.)
Bojao se? (colloq.)
However, with just the present forms of biti, there are questions like this often heard:
Jeste gladni? ▶ (colloq.)
All the ways of making questions described above are used in the real life, unlike some formal terms that actually nobody uses (e.g. formal hladnjak vs. colloq. frižider fridge). For example, here are some statistics (by Google™ search) from the Croatian discussion site, forum.hr:
|jesi li gledala||3280|
|da li si gledala||1420|
There's another, special type of questions, asking for advice or an opinion. In English, such questions begin with Should I... or something like it. In Standard Croatian, you can start such questions with da li da + present, but that works for the present tense only:
Da li da gledam taj film? Should I watch that movie?
In the past tense, you have to use the verb trebati need/should + verb in infinitive; questions follow the same pattern as any other yes/no question:
Jesam li trebala gledati taj film? Should I have watched that movie?
(How to use infinitives will be explained a bit later.)
Colloquially, da li is very often left out in such opinion questions, and you'll most of the time hear and see just:
Da gledam taj film? (colloq.) Should I watch that movie?
Sometimes you'll hear jel instead of da li even in opinion questions:
Jel da gledam taj film? (colloq.) Should I watch that movie?
Such opinion questions are often answered with conditionals and imperatives – verb forms I haven't introduced yet. (For conditionals, check as 38 Would, Could: Conditionals; for imperatives, see 53 Giving Orders.)
® This way of making questions is considered standard in Bosnia and Serbia, and it's often considered (or was often considered) standard in Croatia as well.