Arrays - potatoscript/dsa GitHub Wiki

📦 What is an Array?

Imagine a row of mailboxes 📬 lined up neatly.

Each box:

Has its own number (called index),
Can hold one item (like a number, word, or toy),
Is placed side by side in one long row.

That’s an Array in computer land! 💻

+-----+-----+-----+-----+-----+
|  10 |  20 |  30 |  40 |  50 |
+-----+-----+-----+-----+-----+
   ↑     ↑     ↑     ↑     ↑
 Index 0  1     2     3     4

👆 This is an array with 5 numbers.

🧠 Why Do We Use Arrays?

Arrays help us:

Group similar items together 🧸🧸🧸
Access any item instantly by its number (index)
Store data in a fixed, ordered way

🧸 Real-Life Examples

Situation	Array Use
🧁 Cupcakes in a tray	Each cupcake is in a slot (index)
🎒 Pencils in a case	Each pencil has a spot
🧦 Socks in a drawer	Each drawer section = index

🧪 C# Code Example

string[] fruits = { "Apple", "Banana", "Cherry", "Date" };

Console.WriteLine(fruits[0]); // Apple
Console.WriteLine(fruits[2]); // Cherry

🏗️ How Arrays Work in Memory

An array:

Uses contiguous memory (placed side-by-side 🧱🧱🧱)
Is fixed-size (you decide the number of items when you create it)

int[] scores = new int[5];  // Can hold 5 scores

🧮 Indexing – The Secret Key

Index	Value
0	"Cat"
1	"Dog"
2	"Fox"

To get "Dog":

string animal = animals[1]; // Dog

🔑 Index starts from 0!

✨ Fun Array Operations

1. 📥 Add (Set) Value

int[] numbers = new int[3];
numbers[0] = 100;
numbers[1] = 200;
numbers[2] = 300;

2. 📤 Get Value

Console.WriteLine(numbers[1]); // 200

3. 🔁 Loop Through All

for (int i = 0; i < numbers.Length; i++)
{
    Console.WriteLine(numbers[i]);
}

Or the cooler version:

foreach (int num in numbers)
{
    Console.WriteLine(num);
}

💥 What Happens If You Go Too Far?

Console.WriteLine(numbers[10]);

❌ Error! That’s called an IndexOutOfRangeException!
🚫 You tried to open a mailbox that doesn’t exist.

🍕 Arrays of Different Types

You can make arrays of:

🧮 int[] – numbers
🔤 string[] – words
✅ bool[] – true/false

bool[] lights = { true, false, true };

🧠 Array Facts Cheat Sheet

Fact	Meaning
🔢 Indexed	Start at 0
📏 Fixed Size	You can’t change its length
🚀 Fast Access	`O(1)` time to get any item
🐌 Slow Insert/Delete	Need to shift all other items

🧁 How is Array Different From List?

Feature	Array	List
Size	Fixed	Flexible
Speed	Fast	Slower insert/delete
Syntax	Simple	Has more functions

🧱 Visual Breakdown: Storing Student Scores

int[] scores = { 85, 90, 78, 92, 88 };

// Index:   0   1   2   3   4
// Score:  85  90  78  92  88

To get the 3rd student’s score:

int third = scores[2]; // 78

💡 Behind the Scenes: How Computers Use Arrays

Each item has a memory address
Computers calculate the exact address using:
```
address = baseAddress + (index × size)
```
This is why accessing items is super fast!

📐 Big O for Arrays

Operation	Time	Notes
Get item	O(1)	Super fast!
Set item	O(1)	Direct overwrite
Search item	O(n)	Need to scan
Insert/Delete	O(n)	Shift items needed

🚀 Common Mistakes to Avoid

❌ Accessing outside the array:
```
fruits[5]; // ERROR!
```
❌ Changing length after creation:
```
// You can't do: fruits.Length = 10;
```

❌ Confusing Length (property) and Count() (LINQ):

fruits.Length  // ✅
fruits.Count() // Only if you use LINQ

🛠️ Practice Time – Mini Challenges

🥇 Challenge 1

Create an array of 4 animals and print the second one.

🥈 Challenge 2

Make a loop that says hello to 5 different names in an array.

🥉 Challenge 3

What happens when you use index 100 in an array of 3 items?

🧠 Summary – What We Learned

✅ Arrays store multiple items in one place
✅ Each item has an index starting at 0
✅ Fixed size, super fast to access
✅ Commonly used in loops, search, sort, and more