GCSE Link: None

A stack is a static abstract data type which stores a sequence of items.

But while queues use first in first out (FIFO), stacks use last in first out (LIFO).

These are the main operations on a stack:

• push: adds an item to the top of the stack
• peek: returns the top item without removing it
• pop: removes and returns the top item from the stack
• empty: checks if there are no items on the stack
• full: checks if there is no more space on the stack

Stacks are generally depicted vertically, and we use the terms "bottom" and "top" of the stack to mean the start and end of the underlying array.

One common use of stacks is the call stack, which is explained in 9.07 (Recursion).

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What are some other uses of stacks?

E.g., for browser histories (in the back button), or for undo sequences.

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