She said she'd come later 나중에 온대
She said she was late 늦었대
She said she wasn't feeling well so she won't be going to class tomorrow 얘가 아파서 내일에 학교에 안 간대
I said 'I am eating'
I would say "먹고 있다고 했어" since it's in progressive tense. The person who said 'I am eating' is the first person so you can't use -대 in this case.
He said he ate it but he didn't
얘가 먹었대지만 안 먹었어
얘가 먹었대는데 안 먹었어
얘가 먹은 것이라고 했는데 안 먹었어
먹었대지만 and 먹었대는데 are informal but both are OK when spoken, I think. Or to make it clearer:
"얘가 먹었다고 했는데 / 먹었댔는데, (사실은) 안 먹었어"
He said he was going to eat it but he didn't in the end 얘가 먹은대지만 결국 안 먹었어
"얘가 먹는댔지만 결국 안 먹었어". 먹은대지만 doesn't make sense
Can I combine ~대 with 는데/지만?
Yes. -대는데/-대지만 are spoken in everyday conversation but -다는데/-다지만 is the correct formal form.
Is there a difference between 데 and 대? For example instead of saying 온대 I say 온데.
데 and 대 are totally different. 온대 is a shorthand for "온다고 해" while 온데 does not even make sense.
Please give me some examples with ~대 that covers past, present and future tense if you can.
친구가 거기 갔대 (A friend of mine said he went there)
친구가 거기 가고 있대 (A friend of mine said he was going there)
친구가 거기 간대 (갈 거래) (A friend of mine said he would go there)