Japanese Dewa nai and Dewa naku?

Question:

Whats the difference? Are they used the same?

Answer:

They're practically the same.

For grammatical purposes in Japanese,

the"i" sound, is conjugated to a "ku" sound.

However, since dewa nai and dewa naku means "it is not" it probably doesn't work here. You often see dewa naku in rarely but some formal conversation, or in song lyrics, or in casual conversations. Sometimes when you translate things or make sense of it, it's best not to think about it too much.