Quiz Entry - updated: 2026.09.29
What is the Stack ADT, and what are its operations?
A stack stores objects in last-in, first-out (LIFO) order: push(o) puts an element on top, pop() removes and returns the top element. Helper operations are top() (look without removing), size() and isEmpty().
Picture a stack of plates: you can only put a plate on top and only take the top one. The most recently added element is always the first to come out.
| Operation | What it does |
|---|---|
push(o) |
insert o on top |
pop() |
remove and return the top element |
top() |
return the top element without removing it |
size() |
number of stored elements |
isEmpty() |
whether any elements are stored |
Only the top is accessible. There is no operation to read the element at the bottom or in the middle, and that restriction is what makes a stack so cheap to implement: every operation touches one end.
Go deeper:
Stack (abstract data type) — operations, array and linked implementations, and applications.
Stack visualisation, array-based (USF) — push and pop and watch the top index move.