In an interview, it is perfectly fine to not indent or comment your code. In fact, I would be surprised if you had time to do that-- we normally don't give that much time.
As a general practice, however, I fully expect you to indent your code and add comments where necessary. In fact, our build machine will fail on minute things like including tabs instead of spaces in your code.
Code readability is important. Just like no one likes reading one big paragraph (instead of small, structured paragraphs), no one likes reading one big lump of code with no formatting.
