Question marks at the end of declarative sentences [duplicate]
Solution 1:
As Brian says, this is non-standard. It should not be used in formal writing.
You are correct, though, that ending a declaration with a question mark is used to imply a related question. "I'm out of ideas?" is intended to mean "I'm out of ideas, do you have any?" or "I'm out of ideas, can you help?"
"I'm out of ideas?" uses the question mark improperly, since it's reserved for when you actually ask a question, but it would generally be understood by native English speakers.
Definitely refer to the question RegDwight linked: Is the question mark misused in affirmative sentences?
Solution 2:
No, this is most certainly not standard English grammar. The intention of the question mark at the end of what is clearly a statement is to express the notion that the portion of the statement following the conjunction is unexpected. However, this should be (and is) conveyed by the use of a contravening conjunction (but, however, etc).
Thus, it is not only incorrect but completely unnecessary to conclude statements like the ones in your example with a question mark.
Solution 3:
I agree with what Matthew Read said in his comment/answer.
I'd like to add another thing that came to my mind, though. Look at the following dialogue:
- Did you try to wash it? (just an example)
- Of course I did? -or- Yeah?
Here the second speaker is not asking for further ideas, but instead is expressing sarcasm, something like "of course I did, why are you even asking?"