Stack: Push, Pop and Peek

CSC-211 · Semester III · Data Structures and Algorithms

beginner20 minAvailable

StackLIFO · push / pop / peek · O(1)

empty

top (null)

Top of stack

—

Lab brief

Objective

Understand the LIFO discipline of a stack by performing push, pop and peek, and watching the top pointer move.

Theory & concepts

A stack is a last-in, first-out (LIFO) collection. Push adds an element onto the top, pop removes the top element, and peek reads it without removing. All operations run in O(1) and touch only the top — you cannot reach into the middle. Pushing onto a full stack is overflow; popping an empty stack is underflow.

Rendering diagram…

Stack: push, pop, peek and error conditions

Push  → top := top + 1; arr[top] := value
Pop   → value := arr[top]; top := top - 1
Peek  → arr[top]
All operations are O(1).

Prerequisites

Lesson: Arrays and the linked list family
Concept of last-in-first-out ordering

Instructions

1Push values one at a time and watch them stack above the bottom pointer.
2Pop and watch the top return and the pointer drop.
3Peek without popping and confirm the top is unchanged.
4Push past capacity to observe overflow, and pop past empty to observe underflow.

Tasks

Push a sequence
Push 5, 10, 15 and note the order of the stack top.
Pop back out
Pop twice and confirm the values come out in reverse order (15, 10).
Overflow / underflow
Demonstrate both error conditions and state what the sim does.

Self-check

Push and pop maintain LIFO order.
The student explains why all stack operations are O(1).
Overflow and underflow conditions are correctly identified.

Environment

stack viewpushpoppeektop pointer