📘 Day 5 – Arrays in Data Structures

🚀 What Are Arrays?

An array is a linear data structure used to store multiple elements in a single variable, arranged in an ordered list. Each element is accessed using its index (position).

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🧠 Why Use Arrays?

Imagine storing 100 test scores. Instead of creating 100 variables, you can store them all in one array.

jsCopyEditlet scores = [85, 90, 78, 92, 88];

Now you can access any value using its index:

jsCopyEditconsole.log(scores[0]); // 85

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🛠️ How Arrays Work

• Arrays in JavaScript are zero-indexed.

• This means the first element is at index 0, the second at 1, and so on.

• You can store any type of data in a JS array.

jsCopyEditlet mixed = [42, "hello", true, null];

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📦 Array Operations

1. Create an Array

jsCopyEditlet fruits = ["Apple", "Banana", "Mango"];

2. Access Elements

jsCopyEditconsole.log(fruits[1]); // Banana

3. Change an Element

jsCopyEditfruits[1] = "Orange";

4. Length of Array

jsCopyEditconsole.log(fruits.length); // 3

5. Add Elements

• At the end: push()

• At the beginning: unshift()

jsCopyEditfruits.push("Grapes");
fruits.unshift("Pineapple");

6. Remove Elements

• From the end: pop()

• From the beginning: shift()

jsCopyEditfruits.pop();
fruits.shift();

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🔄 Loop Through Arrays

jsCopyEditfor (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

Or using for...of loop:

jsCopyEditfor (let fruit of fruits) {
  console.log(fruit);
}

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📚 Real-World Analogy

Think of an array like a row of mailboxes — each box (index) stores one item (value). You can open a specific box by its number (index) and retrieve or update the content.

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🔍 Summary

• Arrays store ordered lists of items.

• Indexing starts from 0.

• You can add, remove, access, and loop through items.

• They’re used everywhere — from handling user data to game inventories and more.

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🧪 DSA CHALLENGES

✅ Easy:

Print the first and last elements of an array.

jsCopyEditlet cities = ["Lagos", "Abuja", "Kano", "Ibadan"];

⚙️ Intermediate:

Write a loop that prints only the even numbers from an array:

jsCopyEditlet numbers = [2, 5, 8, 9, 12, 15, 20];

🔥 Hard:

Reverse an array manually (without using reverse()):

jsCopyEditlet data = [1, 2, 3, 4, 5];

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✅ Solutions

• Easy:

    jsCopyEditconsole.log(cities[0], cities[cities.length - 1]); // Lagos Ibadan
  

• Intermediate:

    jsCopyEditfor (let num of numbers) {
      if (num % 2 === 0) {
        console.log(num);
      }
    }
  

• Hard:

    jsCopyEditlet reversed = [];
    for (let i = data.length - 1; i >= 0; i--) {
      reversed.push(data[i]);
    }
    console.log(reversed); // [5, 4, 3, 2, 1]
  

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