Lesson 6: Arithmetic Operators

Arithmetic Operators

Python supports all standard mathematical operations you're familiar with. These operators allow you to perform calculations and manipulate numeric values in your programs.

Understanding arithmetic operators is fundamental to programming, as they're used in almost every program for calculations, comparisons, and data manipulation.

arithmetic.py
a = 10
b = 3

print(a + b)   # Addition: 13
print(a - b)   # Subtraction: 7
print(a * b)   # Multiplication: 30
print(a / b)   # Division: 3.333... (always returns float)
print(a // b)  # Floor Division: 3 (integer division, rounds down)
print(a % b)   # Modulus (remainder): 1 (10 ÷ 3 = 3 remainder 1)
print(a ** b)  # Exponentiation: 1000 (10 raised to the power of 3)

Detailed Operator Explanation

Let's break down each operator with more examples:

operators_detail.py
# Addition (+)
print(5 + 3)        # 8
print(10.5 + 2.3)   # 12.8

# Subtraction (-)
print(10 - 4)        # 6
print(5 - 10)        # -5

# Multiplication (*)
print(4 * 7)        # 28
print(3.5 * 2)      # 7.0

# Division (/) - always returns float
print(10 / 2)        # 5.0 (float, not int!)
print(9 / 2)         # 4.5

# Floor Division (//) - rounds down to integer
print(10 // 3)       # 3 (not 3.333)
print(17 // 5)       # 3

# Modulus (%) - returns remainder
print(10 % 3)        # 1 (10 ÷ 3 = 3 remainder 1)
print(15 % 4)        # 3 (15 ÷ 4 = 3 remainder 3)
print(8 % 2)         # 0 (even number, no remainder)

# Exponentiation (**) - power operation
print(2 ** 3)        # 8 (2 to the power of 3)
print(5 ** 2)        # 25 (5 squared)
print(16 ** 0.5)     # 4.0 (square root of 16)

Assignment Operators

Assignment operators provide shortcuts for updating variables. They combine an arithmetic operation with assignment:

assignment.py
x = 10

# Equivalent to: x = x + 5
x += 5   # x is now 15
print(x)

# Equivalent to: x = x - 3
x -= 3   # x is now 12

# Equivalent to: x = x * 2
x *= 2   # x is now 24

# Equivalent to: x = x / 4
x /= 4   # x is now 6.0

# Equivalent to: x = x // 2
x //= 2  # x is now 3.0

# Other assignment operators
y = 5
y %= 3   # y = y % 3 → y = 2
z = 2
z **= 3  # z = z ** 3 → z = 8

Operator Precedence (Order of Operations)

Python follows standard mathematical order of operations. When an expression has multiple operators, Python evaluates them in a specific order:

📐 Order of Operations (PEMDAS)

Parentheses (highest priority)

Exponents (**)

Multiplication, Division (*, /, //, %)

Addition, Subtraction (+, -)

precedence.py
# Multiplication happens before addition
print(2 + 3 * 4)     # 14 (not 20)
# Calculated as: 2 + (3 * 4) = 2 + 12 = 14

# Parentheses override precedence
print((2 + 3) * 4)   # 20
# Calculated as: (2 + 3) * 4 = 5 * 4 = 20

# Exponents evaluate right to left
print(2 ** 3 ** 2)   # 512 (not 64)
# Calculated as: 2 ** (3 ** 2) = 2 ** 9 = 512

# Complex expression
result = (2 + 3) * 4 ** 2 - 10
# Step 1: (2 + 3) = 5
# Step 2: 4 ** 2 = 16
# Step 3: 5 * 16 = 80
# Step 4: 80 - 10 = 70
print(result)  # 70

Practical Examples

Here are real-world examples using arithmetic operators:

practical.py
# Calculate total price with tax
price = 100
tax_rate = 0.08  # 8% tax
total = price + (price * tax_rate)
print(f"Total: ${total}")

# Calculate area of a rectangle
length = 10
width = 5
area = length * width
print(f"Area: {area} square units")

# Check if number is even (modulus with 2)
number = 42
if number % 2 == 0:
    print("Even number")

# Calculate average
scores = [85, 90, 88]
average = (scores[0] + scores[1] + scores[2]) / 3
print(f"Average: {average}")

Important Notes

💡 Division Always Returns Float

Regular division (/) always returns a float, even if the result is a whole number. Use floor division (//) if you need an integer result.

💡 Modulus is Useful

The modulus operator (%) is great for checking if numbers are even/odd, wrapping around values, and many other useful patterns.

💡 Use Parentheses for Clarity

When in doubt, use parentheses to make your expressions clear. It's better to be explicit than to rely on operator precedence!

Arithmetic Operators

Arithmetic Operators

Detailed Operator Explanation

Assignment Operators

Operator Precedence (Order of Operations)

📐 Order of Operations (PEMDAS)

Practical Examples

Important Notes

💡 Division Always Returns Float

💡 Modulus is Useful

💡 Use Parentheses for Clarity

Lesson Complete!