The correct sentence is: I didn't see anything . Cause In standard English grammar, double negatives (like "didn't" and "nothing" used together) are considered incorrect because they cancel each other out, making the meaning positive (which is not what you intend). So, "I didn't see nothing" would technically mean "I saw something," which is not the intended meaning. The correct construction is "I didn't see anything," where "didn't" (a negative) pairs with "anything" (a non-negative word that works in negative sentences), to express that you saw nothing.

I would say the double negative is not incorrect, if it's intonated correctly, it's a popular valid slang, spoken so widely it should be acknowledged and accepted. I would just say it's not formal English, rather than it's not correct.