Chapter 3: Input & Output

# f-strings: the modern way to format output
name = "Alice"
age = 15
school = "Greenwood Academy"

print(f"My name is {name} and I am {age} years old.")
print(f"I attend {school}.")
print(f"Next year I will be {age + 1}!")

# String concatenation: joining strings with +
first_name = "Priya"
surname = "Sharma"

# Joining strings together
full_name = first_name + " " + surname
print("Full name: " + full_name)

# You can build up longer messages
greeting = "Hello, " + full_name + "! "
greeting = greeting + "Welcome to Python."
print(greeting)

# In a real Python program, you would write:
#   name = input("What is your name? ")
#   colour = input("What is your favourite colour? ")
# But since we're running in the browser, we set values directly:

name = "Jordan"       # Try changing this to your name!
colour = "turquoise"  # Try changing this to your favourite colour!

# Now we use the variables just as if the user had typed them
print(f"Hello, {name}!")
print(f"Ah, {colour} is a lovely colour.")
print(f"Here's a fun fact, {name}: Python was named after Monty Python!")

# \n creates a new line inside a string
print("Line one\nLine two\nLine three")

print()  # blank line to separate examples

# \t inserts a tab (useful for aligning columns)
print("Name\tAge\tCity")
print("Alice\t15\tLondon")
print("Ben\t14\tManchester")

print()

# \\ prints a literal backslash
print("The file is at C:\\Users\\student\\homework.py")

# \" lets you include double quotes inside a double-quoted string
print("She said, \"Python is brilliant!\"")

# Alternatively, mix quote types to avoid escaping
print('She said, "Python is brilliant!"')

# The .format() method — the older way to format strings
name = "Marcus"
age = 16
subject = "Computer Science"

# Positional placeholders (filled in order)
print("Hello, {}! You are {} years old.".format(name, age))

# Numbered placeholders (you choose the order)
print("{0} studies {1}. {0} is {2}.".format(name, subject, age))

# Named placeholders (most readable version)
print("Student: {n}, Subject: {s}".format(n=name, s=subject))

# Formatting numbers with .format()
price = 19.5
print("The total is £{:.2f}".format(price))

# Simple calculator — simulating user input
# In real Python: num1 = float(input("Enter first number: "))
num1 = 24.5
num2 = 7

# Perform all four basic operations
addition = num1 + num2
subtraction = num1 - num2
multiplication = num1 * num2
division = num1 / num2

# Display results with neat formatting
print("=" * 30)
print("   SIMPLE CALCULATOR")
print("=" * 30)
print(f"  First number:  {num1}")
print(f"  Second number: {num2}")
print("-" * 30)
print(f"  Addition:       {addition}")
print(f"  Subtraction:    {subtraction}")
print(f"  Multiplication: {multiplication}")
print(f"  Division:       {division:.2f}")
print("=" * 30)

# === BMI Calculator ===
# In real Python:
#   weight = float(input("Enter your weight in kg: "))
#   height = float(input("Enter your height in metres: "))

weight = 65.0   # kilograms — try changing this!
height = 1.72   # metres — try changing this!

# Step 2: Calculate BMI
bmi = weight / (height ** 2)

# Step 3: Display formatted result
print("=" * 32)
print("     BMI CALCULATOR")
print("=" * 32)
print(f"  Weight: {weight} kg")
print(f"  Height: {height} m")
print("-" * 32)
print(f"  Your BMI is: {bmi:.1f}")
print("-" * 32)

# Step 4: Classify the result
if bmi < 18.5:
    category = "underweight"
elif bmi < 25:
    category = "healthy weight"
elif bmi < 30:
    category = "overweight"
else:
    category = "obese"

print(f"  Category: {category}")
print("=" * 32)
print()
print("Note: BMI is a rough guide only")
print("and does not account for muscle,")
print("age, or other important factors.")