Publishing a conference version of a journal paper at the same time ? (copyright issues) This may be a question repeated many times, but I want to know your opinion. 

I submitted a journal paper for an algorithm (Computer Science). Fearing that the review process take too long, I decided to submit a short-version conference paper, while the long version is under-review. I received the journal review comments, and re-sent the modifications to the journal. Meanwhile, the conference paper was accepted. But the camera-ready is not sent yet. 

The problem is that both papers are about the same idea. There is also some copy-pasted parts in both papers. But:

1) the editor of the journal was not informed about the conference paper (I heard that I should tell the journal about any published papers - but note that the conference paper is not yet published - not even the camera ready is submitted), 

2) the organization organizing the conference, is not the same that manage the journal. I have been told that there are conflicting copyrights. 

The proposed solutions (that colleagues told me about): 

a) submit both as is ! 

b) submit both (but with change in text). 

c) do not submit the conference paper (but I heard this can be harmful)

d) tell the editor now (but honestly, the journal is way more important than the conference).
The problem is that you have painted yourself into a corner.

You have made a very serious mistake by submitting simultaneously to a conference (with formal proceedings) and a journal. Most likely both the conference and the journal have explicit rules forbidding this, and in any case any kind of simultaneous submission is highly unethical: you are abusing the peer-review system.

No matter what you do, someone will be upset.

If you are a student, perhaps the best approach is to play stupid. Contact the conference organisers, apologise sincerely, explain that you were not aware that simultaneous submissions are not permitted, explain that you are just a student, apologise again, and withdraw the conference paper.

The conference organisers will be upset. But maybe this is much better in the long run than proceeding with the publication of both versions, in which case you will make your mistake public and anyone is able to see it (conference submission &amp; acceptance dates are public information, and journals typically publish the submission &amp; acceptance dates of the articles).