Hi, there!
I did the second exercise from the lesson "In the library" and I'd like to get feedback if it's correct. I have some doubts here and there.

1/Yesterday I went to school.
きのうぼくわがっこうにいっきました。
2/ Did you eat any oranges?
あなたわオレンジをたべましたか。
3/ No, the cat wasn't under the table.
いええ、ねこわつくえにのしたにわありませんでした。
4/ Excuse me, where was the big building next to the park?
すみません、おおきいとてもののこうえんのそぼにわどこですか。
5/ I bought trousers the other day.
おとといわたしわズボンをかいました。

Try this:
1/ 昨日、私は学校に行きました。
2/ あなたはいくつかのオレンジを食べましたか？
3/ いいえ、猫がテーブルの下ではなかったです。
4/ すみません、公園近くの大きな建物はどこにありましたか？
5/ 一昨日、私はズボンを買いました。
Pay attention to the particle は

Thanks! Though I have a few questions:

- Why do you put a comma after time adverbs(ex. yesterday)?
- Is omitting the question mark at the end of a sentence considered a mistake? I have a "Learn Japanese"-type textbook in which they don't put ? at the end. At least as far as I've read. But I've seen it around on the net.
- は is used instead of わ to mark a grammatical particle but only then, right?
- いくつかのオレンジ would mean 'some/any oranges'(depending on negative or positive sentence), right?

The comma isn't mandatory. This is just to lighten the sentence.
The question mark at the end of the sentence isn't mandatory. The particle "ka" (か) serves as a question mark.
That's right ! "ha" is the particle and not the syllable "wa".
The particle "ha" (は) is pronounced "wa" (わ) and wrote "ha", "he" (へ) is pronounced "e" (え) and writing "he", "wo" (を) is pronounced "o" (お) and wrote "wo".
Yes, it depends on the use: some, any, a few, a bit (for uncountable), somewhat (to a certain extent).

I see.
Thank you, shiroiookami.