We’ll work through the material **one concept at a time**, and I’ll wait for your answers before moving forward. Since your final instruction says to continue through Chapter 10, I’ll use the course’s sequence of ten major topics as our roadmap: algorithm analysis, array-based lists, linked lists, stacks/queues, priority queues, ordered sets/maps, unordered sets/maps, Unix processes, signals, and Unix I/O. ECE 340 - Spring 2026 - Lecture… # Chapter 1 — Foundations ## Concept 1: What is a Data Structure? At the most basic level, a **data structure** has two parts: **the data itself + the operations you are allowed to perform on that data.** The lecture defines it as a representation of data together with the operations allowed on that data. It also notes that textbooks may describe this combination as an **Abstract Data Type**, or **ADT**. ECE 340 - Spring 2026 - Lecture… Think about a normal integer in C. There is a way the integer is represented, and there are operations you can perform on it. For example, the lecture gives: ```text Data Representation Operations int + - * / % ``` So an `int` is not just some number sitting in memory. There are also operations that make that data useful. The same idea scales up to more complicated structures. For example, the lecture uses a **Stack**: ```text Stack Representation: array or linked list Operations: push, pop, peek, size ``` The important idea is that the **stack is the concept**, while an array or linked list can be the way we actually store the stack internally. That distinction will become very important later. ### Simple example Imagine we want to store this sequence: ```text 10 20 30 ``` We could store those values using an **array-based list**. The values are the **data**. Then the list gives us operations such as: ```text get set append insert remove search ``` Later in the course, the Array-Based Lists lecture specifically describes these kinds of operations for a list. ECE 340 - Fall 2025 - Lecture 5… So you can think: ```text DATA 10 20 30 + OPERATIONS get append remove search ... = DATA STRUCTURE ``` ## How this connects to the rest of the course Almost everything we study later follows this exact idea. A **linked list** stores a collection of items and connects them using links from one item to the next. The lecture compares it to a treasure hunt: you start at the beginning, and at each stop you find both an item and the clue telling you where to go next. ECE 340 - Fall 2025 - Lecture 6… A **stack** has operations such as `push`, `pop`, and `peek`. A **queue** has operations such as `enqueue` and `dequeue`. A **priority queue** removes the highest-priority item first. So throughout ECE 340, we will repeatedly ask two questions: **How is the data stored?** and **What operations can we perform on it?** Later, algorithm analysis will add a third major question: **How expensive are those operations?** That is why data structures and Big-O analysis are closely connected. ## Common mistakes One common mistake is thinking that a data structure is **only the data**. For example, an array of integers is not the entire idea behind an array-based list. The list also specifies the behaviors and operations that go with the stored data. Another common mistake is confusing the **abstract structure** with its **implementation**. For example: ```text Stack ≠ Array ``` A stack can be implemented using an array **or** a linked list. The stack describes how the collection behaves; the array or linked list describes how we store it. This distinction becomes especially important when we later compare multiple implementations of the same ADT. --- ## Check your understanding Answer these **without looking for the answers**. Short answers are fine. **1. Basic recall:** In your own words, what are the **two main parts** of a data structure? **2. Conceptual:** Suppose I tell you that a stack supports: ```text push pop peek size ``` Are those the **data** or the **operations**? **3. Conceptual:** If one stack is implemented using an array and another stack is implemented using a linked list, are they necessarily two completely different ADTs? Explain why or why not. **4. Application:** Imagine a structure containing: ```text [12, 5, 18] ``` and it supports: ```text append remove search ``` Identify: ```text Data = Operations = ``` **5. Explain it yourself:** Finish this sentence as if you were explaining it to someone who has never taken ECE 340: > “A data structure is basically…” Answer **1–5**, and I’ll check each one before we move to the next concept.