Stacks

This lesson covers the stack — a fundamental Abstract Data Type (ADT) that follows the Last-In, First-Out (LIFO) principle. Stacks are used extensively in computing, from managing function calls to evaluating expressions.

---

What is a Stack?

A stack is an ordered collection of elements where:

• Items are added (pushed) to the top of the stack.
• Items are removed (popped) from the top of the stack.
• The most recently added item is always the first to be removed — LIFO.

Think of a stack of plates: you always add to the top and remove from the top. You cannot access plates in the middle without removing the ones above.

TOP →  [ 30 ]
       [ 20 ]
       [ 10 ]
BOTTOM

---

Stack Operations