Which data structure stores items using last-in, first-out semantics?

• A. Queue
• B. Stack
• C. Graph
• D. Array

Answer: (B)

A stack is designed for last-in, first-out behavior. In a stack, you add items with push and remove them with pop, so the most recently added item is the first to come off. This makes it perfect for scenarios where you need to reverse order or unwind steps, such as evaluating nested expressions, tracking function calls, or implementing undo functionality.

A queue, by contrast, follows first-in, first-out, so items exit in the same order they entered. An array is a general storage structure with random access, and while you can use it to implement a stack, it doesn’t inherently enforce LIFO on its own. A graph organizes data as nodes and edges and isn’t a linear storage with a fixed removal order.