Binary & Data

# Binary & Data

Week 2

---

## Review

![](https://media1.giphy.com/media/v1.Y2lkPTc5MGI3NjExbmg4bHN4N2Z4OHN0NHh0OHhnZmk5cm95MndxenE1bmtmazIzdnRmOSZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/gEvab1ilmJjA82FaSV/giphy.webp)

### Four Roles of a Computer?

- Input 
- Storage 
- Processing 
- Output

NOTE: Input, storage, processing, output

### Hardware vs. Software?

- Hardware: _The physical parts of a computer_ 
- Software: _The programs that run on the hardware_

---

## How Computers Store Information

Numbers!

Specifically, **binary** numbers.

Decimal: base-10

> 1, 2, 3, 4, 5...

Binary: base-2

> 1, 10, 11, 100, 101...

NOTES:
- What other words start with "bi?"
- What is another base you could count with?

### Bits

A bit is a single binary digit: either 0 or 1.

### Bytes

A byte is 8 bits.

`00000000` is 0 in decimal

`11111111` is 255 in decimal

NOTES: why 8? because it's a power of 2 (2^3)

---

## Representing Data

### Integers

Binary numbers work just like decimal numbers, but with only two digits (0 and 1) instead of ten.

## Negative Integers

How do you store the number -42?

> <mark>0</mark>0100101 = 37
>>
> <mark>1</mark>0100101 = -37

## Exercise

Invent a method to store rational numbers in binary

NOTES:
- Rational numbers = "any number that can be written as a fraction"
- Serialization = "translating data into a format that can be stored and reconstructed later"
- Split into teams
- Have each time serialize a fraction, other team deserializes
- What are the limitations of your method?

### Floating Point

How do you store a number like 3.14?

![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fmedia.geeksforgeeks.org%2Fwp-content%2Fuploads%2F20240503164047%2FFloating-Point-Representation.webp&f=1&nofb=1&ipt=6e51cd6aeb8423e1de980f9f93ec27130fc4ca257347a9bbb5e02e2744192531)

NOTE: You do **not** need to remember this!

### Floating Point

![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Ftrekhleb.dev%2Fstatic%2F131599cc123194bea250477696211e3a%2Fe8950%2F02-half-precision-floating-point-number-explained.png&f=1&nofb=1&ipt=6cefbf29fed924bf58f660bf7441afde1ae926df56fcac938373da627fefd2c2)

### Letters

Assign each letter a number.

> "Hello" = 72 101 108 108 111

NOTES:
- This is called a "character encoding"
- ASCII is the most common one for English text
- For example, the letter "A" is number 65

---

## Variables

### What is a Variable?

A name for some data.

NOTES:
Think of it like a "bucket" or a "handle"

### Naming Things

> There are only two hard things in Computer Science: cache invalidation and **naming things**.

NOTES: This is a famous quote in programming. Good naming is hard but really important.

### Python Naming Rules

- Must start with a letter or underscore (`_`)
- Can contain letters, numbers, and underscores
- Cannot contain spaces or special characters
- Case-sensitive: `name` ≠ `Name`
- By convention, use `snake_case` (lowercase with underscores)

```py
# Good names
student_name = "Alice"
age_in_years = 15
_private_value = 42

# Bad names
sn = "Alice"           # too short
studentName = "Alice"  # camelCase, not Pythonic
s n = "Alice"          # space, won't work
2fast = 100            # starts with number
```

NOTES: Show that Python enforces some rules (syntax errors for spaces/numbers at start) but others are conventions (snake_case).

### Exercise: Name These Variables

Suggest good variable names for:

1. A student's favorite color 
2. The number of books in a library 
3. Whether a user is logged in 
4. A person's email address

NOTES:
- favorite_color
- total_books or num_books
- is_logged_in (boolean convention: starts with "is_" or "has_")
- email_address or user_email

### Two Types of Variables

- Primitive 
- Compound

### Primitive Data Types

- Integer (int) 
- Floating Point Number (float) 
- String (str) 
- Boolean (bool) 
- NoneType (None)

### Example

```py
100             # integer
3.14            # float
"Hello, World!" # string
True            # bool
None            # None
```

### Exercise: Choose a Data Type

What primitive data type would you use to store:

1. A person's age 
2. A product's price 
3. A user's name 
4. Whether an account is premium 
5. The result of a calculation that hasn't been computed yet

NOTES:
- age: int
- price: float
- name: str
- premium: bool
- result: None (use as a placeholder)

### What's Hard to Store with Primitives?

Think about data that would be difficult to represent with just a single primitive type.

NOTES:
Example 1: A student's schedule. You'd need to store the course name (string), time (maybe a string or int for hours), room number (int), and instructor name (string). A single primitive type can't hold all of that together.

Example 2: A restaurant's menu item. You'd need the dish name (string), price (float), ingredients (multiple strings), and whether it's vegetarian (bool). Again, primitives alone aren't enough.

This is why we need compound data types like lists and dictionaries.

### Compound Data Types

- Lists 
- Tuples 
- Dictionaries 
- Sets

### Example

```py
[1, 2, 3]             # list
(1, 2, 3)             # tuple
{"one": 1, "two": 2}  # dictionary
{1, 2, 3}             # set
```

### Reassignment

Will this code throw an error?

```py
year = 2026
year = "crazy"
```

No ✅

### Reassignment

Will this code throw an error?

```py
year = 2026
message = year + " is crazy"
```

Yes 💥 Instead, do this:

```py
year = 2026
message = str(year) + " is crazy"
```

---

![](https://media4.giphy.com/media/v1.Y2lkPTc5MGI3NjExd2NmamM3NmR2c3RtenR3bGV5dnR1MnNyM3BzNnh3ZGNwYTFyZ2V6YyZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/uSZQ6WPIcpouUEpNTe/giphy.gif)