Stacks

This lesson covers stacks — an essential abstract data type (ADT) in the OCR A-Level Computer Science (H446) specification. Stacks are used extensively in computing, from function call management to expression evaluation.

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What is a Stack?

A stack is a linear data structure that follows the LIFO (Last In, First Out) principle. The last item added to the stack is the first item to be removed — like a stack of plates.

Real-World Analogies

• A stack of plates: you add to the top and take from the top.
• The "Back" button in a browser: returns to the most recently visited page.
• An undo feature: reverts the most recent action first.

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Stack Operations