Data StructureBeginner

Arrays

A row of lockers for your data

3–5 hours 10 LeetCode

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What is it?

An array is like a row of lockers numbered from 0.

Each locker has a number (the index) — so you can jump to any locker instantly.
You can open any locker quickly if you know its index.
The items stay in order from left to right.

In programming, arrays are great when you want fast access and simple iteration.

Variants / Subtypes

Static array — fixed size, memory allocated upfront (e.g. Java int[])
Dynamic array — can grow automatically, like JavaScript arrays or Python lists

Real-World Examples

Seats in a cinema row

Student marks list

Daily temperatures

Monthly sales figures

Game scoreboard

Shopping product list

How It Works — Visualized

▶

Interactive Visualizer

— step through with real data

Array [15, 3, 9, 7, 21, 4, 11] — each element at a fixed index

1/7

Code Example

What this code shows

Start with [1, 2, 3]. Add 4 to the end and 0 to the front, giving [0,1,2,3,4]. Remove from both ends, leaving [1,2,3]. Check if 2 exists, then print each item.

const arr = [1, 2, 3];

arr.push(4);       // add to end   → [1, 2, 3, 4]
arr.unshift(0);    // add to front → [0, 1, 2, 3, 4]
arr.pop();         // remove last  → [0, 1, 2, 3]
arr.shift();       // remove first → [1, 2, 3]

console.log(arr.includes(2)); // check membership → true

// iterate and print each item
for (const x of arr) {
console.log(x);  // 1, then 2, then 3
}

Expected Output

true
1
2
3