What exactly are hashtables?

Question

• What are they and how do they work?
• Where are they used?
• When should I (not) use them?

I\'ve heard the word over and over again, yet I

Answer 1

Wikipedia seems to have a pretty nice answer to what they are.

You should use them when you want to look up values by some index.

As for when you shouldn't use them... when you don't want to look up values by some index (for example, if all you want to ever do is iterate over them.)