Introducing stacks

At its most basic level, a stack is a collection of elements of the same specified type. The length of a stack is variable, meaning it can change depending on how many elements it’s holding. The important difference between a stack and a list or array is how the elements are stored. While lists or arrays store elements by index, stacks follow the last-in-first-out (LIFO) model, meaning the last element in the stack is the first accessible element. This is useful when you want to access elements in reverse order. You should note that they can store null and duplicate values. A helpful analogy is a stack of plates—the last plate you put on the stack is the first one you can easily get to. Once it’s removed, the next-to-last plate you stacked is accessible, and so on.

All the collection types in this chapter are a part of the System.Collections.Generic namespace, meaning you need to add the following code to the top of any file that...