A stack is one of the simplest data structures you will study in this course, and almost all of its behavior follows from a single rule: Last In, First Out, or LIFO. Whatever element was added most recently is the only one you are allowed to remove next, and the only one you are allowed to inspect. That restriction is not a limitation to work around — it is the entire point, because it makes the structure predictable, fast, and a perfect match for problems that unwind in reverse order.
In this topic we define LIFO precisely, ground it in a familiar physical analogy (a stack of plates or trays), and contrast it with other ordering principles you already know — the First In, First Out rule of a queue, and the index-based random access of an array. We then look at the two operations that enforce LIFO, push and pop, and at the idea of the 'top': a single reference or index that marks where the next push lands and where the next pop comes from. Understanding the top is what makes later discussions of constant-time operations and underlying containers make sense.
As you watch the videos below, keep three questions in mind. First, where exactly is the top, and how does it move during a push versus a pop? Second, what happens when you pop an empty stack or push onto a full one — how is that condition detected? Third, what kinds of problems would become harder if you were allowed to reach into the middle of the stack? That last question is the bridge to Module 4's later topics on undo features, call stacks, and expression evaluation.
A concise introductory lecture on the stack as an abstract data type, focused on the push and pop operations that add and remove elements at the top. Based on its title and framing, expect a walkthrough of how elements enter and leave in LIFO order, how the top pointer or index shifts with each operation, and likely mention of overflow and underflow conditions.
Gate Smashers is a widely followed exam-prep computer science channel known for tight, board-style explanations, and at under seven minutes this video gives you a fast, accurate grounding in the two core operations and the concept of the top.
A longer lecture that moves from the theory of stacks, queues, and bags toward how they are actually implemented. The description explicitly contrasts LIFO with FIFO, so expect a side-by-side treatment of the two ordering rules along with discussion of implementation choices and best practices for each structure.
This is the best fit for the 'LIFO vs. other ordering principles' subtopic, since it puts stacks and queues next to each other rather than presenting LIFO in isolation, and it previews the implementation work coming later in the module.
A focused treatment of stacks built around the LIFO principle itself, with code examples noted in C++ and JavaScript plus coding challenges. Expect the definition of LIFO, demonstrations of how pushing and popping behave in code, and examples of where the pattern is useful.
The JavaScript examples connect directly to the language you will use for your own Stack class in this module, and the dedicated emphasis on LIFO makes it a good reinforcement of why the ordering rule matters rather than just how it works.
Together these three videos target MO1 most directly: each defines LIFO and explains the push and pop operations that enforce it, and the Study Hub lecture explicitly contrasts LIFO with the FIFO ordering of a queue, which is exactly the comparison MO1 asks you to make. The emphasis on the top pointer and on overflow and underflow conditions sets up MO3, since constant-time push and pop depend entirely on only ever touching one end of the container. The JavaScript and C++ examples in the Mr. Feynman video preview the class you will build for MO2, and the discussion of why LIFO is useful lays the conceptual groundwork for the application topics in MO4 and MO5, where you will see this same reverse-order behavior driving undo features, call stacks, and expression evaluation.
These videos were chosen from YouTube on October 2, 2026. Each has captions; the player turns them on. Videos on YouTube can be changed or removed — if one no longer plays, tell your instructor. If a player does not appear, use its Watch on YouTube link.