Variables & Data Types

🎒 Real-Life Analogy: Variables are Like Labeled Storage Containers

Imagine you're organizing your room:

• Box labeled "TOYS": Contains your toys - you can put toys in, take them out, replace them
• Jar labeled "COOKIES": Contains cookies - you know exactly what's inside by reading the label
• Folder labeled "HOMEWORK": Contains your homework sheets

Variables work exactly the same way! Each variable is a labeled container that stores data:

• age = 15 - Container labeled "age" stores the number 15
• name = "Krishna" - Container labeled "name" stores the text "Krishna"
• score = 95 - Container labeled "score" stores the number 95

Key point: The label stays the same, but you can change what's inside anytime!

🔍 What Just Happened Behind the Scenes?

1. Variable Creation: When you write name = "Krishna", Python creates a space in memory
2. Storage: The text "Krishna" is stored in that memory location
3. Labeling: Python creates a label called "name" that points to this memory location
4. Reuse: Every time you use name, Python looks up what's stored there

Memory Perspective:

Memory:  [Address 1000] → "Krishna"
Label:   name → points to Address 1000

When you print(name):
1. Python sees "name"
2. Looks up what "name" points to
3. Finds "Krishna" at Address 1000
4. Prints "Krishna"

❌ What's NOT Allowed:

🗂️ Real-Life Analogy: Data Types are Like Different Containers

Think about organizing things in your kitchen:

• Number jar (Integer): Stores whole items - 5 apples, 10 cookies (you can't have 2.5 cookies!)
• Measuring cup (Float): Stores precise measurements - 2.5 cups of flour, 1.75 liters of milk
• Label maker (String): Stores text - recipe names, ingredient labels, notes
• Light switch (Boolean): Only two states - ON or OFF, just like True or False

Why it matters: Just like you wouldn't measure flour with a light switch, Python uses the right data type for each kind of information!

1️⃣ Integers - Whole Numbers

Integers are whole numbers - no decimal point, no fractions.

When to use integers:

• Counting things (number of students, items in cart)
• Ages, years, IDs
• Whole quantities (5 apples, 10 books)

2️⃣ Floats - Decimal Numbers

Floats can have decimal points. Perfect for precise measurements!

When to use floats:

• Money and prices
• Measurements (height, weight, distance)
• Scientific calculations
• Percentages (like 98.6 for temperature)

3️⃣ Strings - Text Data

Strings are text - anything wrapped in quotes!

# String version - treated as text
age_text = "25"
# Can't do: age_text + 1  <- This would cause an error!

# Number version - can do math
age_number = 25
next_year = age_number + 1  # This works! Result: 26

4️⃣ Booleans - True or False

Booleans only have two possible values: True or False

When to use booleans:

• Yes/No questions (Is it raining? True or False)
• On/Off states (Is the light on? True or False)
• Checking conditions (Is age greater than 18?)
• Game states (Is game over? Has player won?)

is_correct = True   # ✅ Correct
is_correct = true   # ❌ Error! (lowercase doesn't work)
is_correct = FALSE  # ❌ Error! (all caps doesn't work)

Understanding the Output:

• <class 'str'> means it's a string (text)
• <class 'int'> means it's an integer (whole number)
• <class 'float'> means it's a float (decimal number)
• <class 'bool'> means it's a boolean (True/False)

Don't worry about the word "class" for now - just focus on the type name inside the quotes!

1️⃣ Converting to Integer - int()

# These work:
int("123")      # ✅ Result: 123
int(45.8)       # ✅ Result: 45 (decimal removed)
int(True)       # ✅ Result: 1
int(False)      # ✅ Result: 0

# These DON'T work:
int("hello")    # ❌ Error! Can't convert text to number
int("12.5")     # ❌ Error! String has decimal point

2️⃣ Converting to Float - float()

3️⃣ Converting to String - str()

This one almost always works! You can convert any type to a string.

Basic input() Example:

Note: The input() function works differently in this web environment. In a real Python program on your computer, it would wait for you to type. Here's how it normally works:

# In a real Python environment:
name = input("What is your name? ")
print("Hello,", name)

# What happens:
# 1. Python displays: "What is your name? "
# 2. Cursor waits for you to type
# 3. You type: Krishna
# 4. You press Enter
# 5. Python stores "Krishna" in the name variable
# 6. Prints: "Hello, Krishna"

age = input("How old are you? ")
# Even if you type 25, age will be "25" (a string), not 25 (a number)

# To use it as a number, convert it:
age = int(input("How old are you? "))
# Now age is 25 (a number) and you can do math with it!

Complete input() Example Pattern:

# Pattern for getting text input:
name = input("Enter your name: ")
print("Welcome,", name)

# Pattern for getting number input:
age = int(input("Enter your age: "))
print("You are", age, "years old")

# Pattern for getting decimal number:
height = float(input("Enter your height in feet: "))
print("Your height is", height, "feet")

# Pattern for calculations:
num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
sum = num1 + num2
print("Sum:", sum)

Pro Tip: Always include a descriptive message in input() so users know what to type!