Guide to English grammar

I didn't see no one. (non-standard) (= I didn't see anyone./I saw no one.)
In standard English a double negative has a different meaning.
I didn't see no one. (= I saw someone.) I saw one of my friends.
We can't do nothing. (= We must do something.)

NOTE
We sometimes use a negative after I wouldn't be surprised if/It wouldn't surprise me if...

I wouldn't be surprised if it rained/if it didn't rain. (The speaker expects that it will rain.)

6 The emphatic negative

1 We can stress not. If we use the short form n't, then we can stress the auxiliary (e.g. did).
Frankenstein did not study medicine.
Frankenstein didn't study medicine.

2 We can use at all to emphasize a negative.

Frankenstein wasn't the name of the monster at all.
There was nowhere at all to park.
Here are some other phrases with a similar meaning.
The operation was not a success by any means. I'm not in the least tired.
The project is not nearly complete. There is still a long way to go.
Her son's visits were far from frequent.
We can use absolutely before no and its compounds.
There was absolutely nowhere to park.

NOTE

1. 
   We can use ever with a negative word.
   

No one ever takes any notice of these memos.

2. 
   We can use whatsoever after “nothing, none, or after no + noun”.
   

There's nothing whatsoever we can do about it.
The people seem to have no hope whatsoever.

For more details about ever and never, •211(1) Note c.

3 An adverbial with a negative meaning can come in front position for extra emphasis. This can happen with phrases containing the negative words no, never, neither, nor, seldom, rarely, hardly and the word only. There is inversion of subject and auxiliary.