🏪 The Magic Store: Understanding Data and Operations

Imagine you own a magical store where you keep track of everything using special boxes and tools. Let’s learn how computers do the same thing!

📦 Variables and Constants: Your Storage Boxes

What Are Variables?

Think of a variable like a labeled box in your room. You can put things inside, take them out, or swap them for something else.

📦 myAge = 10
📦 myName = "Sam"

The box has a name (like myAge), and stuff inside (like 10).

You can change what’s inside anytime:

myAge = 11  ← Birthday! Changed!

What Are Constants?

A constant is a box that’s locked forever. Once you put something in, it stays there. No changes allowed!

🔒 PI = 3.14159
🔒 DAYS_IN_WEEK = 7

Why lock boxes? Some things should NEVER change. The number of days in a week is always 7. Pi is always 3.14159…

graph TD
    A[📦 Storage Box] --> B[Variable: Can change]
    A --> C[Constant: Locked forever]
    B --> D["myScore = 100<br>myScore = 150 ✓"]
    C --> E["MAX_LIVES = 3<br>MAX_LIVES = 5 ✗"]

🎨 Primitive Data Types: The Basic Building Blocks

Just like LEGO has basic brick types (squares, rectangles, flat pieces), programming has basic data types.

Numbers

Integers - Whole numbers (no decimals)

age = 10
score = 9999
temperature = -5

Floats/Decimals - Numbers with dots

price = 19.99
height = 5.7
pi = 3.14159

Text (Strings)

Words and sentences live inside quotes:

name = "Luna"
greeting = "Hello World!"
emoji = "🎮"

True or False (Booleans)

Only two choices - like a light switch:

isGameOver = false
hasWon = true
isRaining = false

Nothing (Null/None)

Sometimes a box is empty on purpose:

middleName = null  ← No middle name!

graph TD
    A[🧱 Primitive Types] --> B[🔢 Numbers]
    A --> C[📝 Strings]
    A --> D[✅ Booleans]
    A --> E[∅ Null]
    B --> F["42, -7, 3.14"]
    C --> G["'Hello', 'World'"]
    D --> H["true, false"]
    E --> I["null, None"]

🎒 Composite Data Types: Boxes Inside Boxes

Sometimes you need to store many things together. That’s where composite types help!

Arrays/Lists

A row of boxes, each with a number:

colors = ["red", "blue", "green"]
         [  0  ] [  1  ] [  2  ]

scores = [100, 85, 92, 78]

Get one item: colors[0] gives "red"

Objects/Dictionaries

Boxes with named labels instead of numbers:

student = {
  name: "Alex",
  age: 12,
  grade: "A"
}

Get one item: student.name gives "Alex"

The Difference

🏷️ Type Systems: The Label Police

Imagine if you tried to add a banana to the number 5. That’s weird, right? Type systems are like police that check if operations make sense.

Static Typing (Strict Police 👮)

You must declare the box type FIRST:

int age = 10;        ✓
age = "ten";         ✗ ERROR! Can't put text in number box

Languages: Java, C++, TypeScript

Dynamic Typing (Relaxed Police 🙂)

The box figures out its type automatically:

age = 10           ← It's a number
age = "ten"        ← Now it's text (allowed!)

Languages: Python, JavaScript, Ruby

Strong vs Weak Typing

Strong: Won’t mix types without permission

"5" + 3 → ERROR! (Python)

Weak: Will try to make it work

"5" + 3 → "53" (JavaScript)

🔄 Type Conversion: Shapeshifting Data

Sometimes you need to change one type into another. It’s like pouring water from a cup into a bottle.

Implicit Conversion (Automatic)

The computer does it for you:

result = 5 + 2.5    ← 5 becomes 5.0 automatically
result = 7.5        ← Now it's a decimal!

Explicit Conversion (You Ask)

You tell the computer to convert:

text = "42"
number = int(text)   ← Convert text to number
result = number + 8  ← Now: 50

Common Conversions

⚠️ Warning: Not all conversions work!

int("hello")  ← 💥 ERROR! "hello" isn't a number

➕ Operators: Your Magic Wands

Operators are symbols that DO things to your data. Like magic wands!

Arithmetic Operators (Math Magic)

Comparison Operators (Question Magic)

Logical Operators (Thinking Magic)

Assignment Operators (Putting Stuff)

x = 10      ← Put 10 in x
x += 5      ← Same as: x = x + 5
x -= 3      ← Same as: x = x - 3
x *= 2      ← Same as: x = x * 2

📊 Operator Precedence: Who Goes First?

When you see 2 + 3 * 4, what’s the answer?

❌ Wrong: (2 + 3) * 4 = 20 ✅ Right: 2 + (3 * 4) = 14

Multiplication goes FIRST! Just like in math class.

The Priority List (Highest to Lowest)

1. Parentheses ( ) - ALWAYS first!
2. Exponents ** - Powers
3. Multiply/Divide * / %
4. Add/Subtract + -
5. Comparisons > < == !=
6. Logical NOT not
7. Logical AND and
8. Logical OR or

Example Breakdown

result = 2 + 3 * 4 ** 2 - 1

Step 1: 4 ** 2 = 16        (exponents first)
Step 2: 3 * 16 = 48        (then multiply)
Step 3: 2 + 48 = 50        (then add)
Step 4: 50 - 1 = 49        (then subtract)

result = 49 ✓

Pro Tip: When in doubt, use parentheses!

result = 2 + (3 * (4 ** 2)) - 1

📝 Expressions and Statements: Sentences of Code

What’s an Expression?

An expression is anything that produces a value. It’s like a math problem that has an answer.

5 + 3           ← Expression (equals 8)
age * 2         ← Expression (equals age doubled)
name == "Sam"   ← Expression (equals true or false)

What’s a Statement?

A statement is a complete instruction. It DOES something.

x = 5 + 3              ← Assignment statement
print("Hello")         ← Print statement
if age > 18:           ← Conditional statement

The Difference

graph TD
    A[Code] --> B[Expressions]
    A --> C[Statements]
    B --> D["5 + 3 = 8"]
    B --> E["age > 18 = true"]
    C --> F["x = 10"]
    C --> G["print#40;x#41;"]
    D --> H[Has a VALUE]
    F --> I[Does an ACTION]

Expressions INSIDE Statements

Statements often contain expressions:

total = price * quantity + tax
        ↑_________________↑
        This is an expression
↑_____________________________↑
This whole line is a statement

🎯 Quick Summary

🚀 You Did It!

You now understand how computers store and work with data. Every app, game, and website uses these exact concepts. When you see code, you’re now seeing:

• Boxes storing things (variables)
• Types telling what’s inside (numbers, text, true/false)
• Operators doing magic on them (+, -, *, ==)
• Rules about who goes first (precedence)
• Instructions making it all happen (statements)

You’re thinking like a computer now! 🧠💻