which saying is right. If both are right, which is better, and what is the difference?
This isn’t really a case of right or wrong. Al you can say is that the contraction (didn’t) is informal and ‘did not’ is formal. You could use the latter if you really wanted to emphasise the negative aspect of the question or statement.
Thanks, Alan. But which saying is more often used. I think we use “didn’t” more often in daily life, am I right?
Yes, you are.