Nested Conditional Execution

Review

• if conditionally executes code
• elif conditionally executes alternative code
• else executes if no other conditions are met

Nesting Conditionals

• We can nest blocks of code
• Conditional execution can be nested to create more complex control flow

Example

if x == y:
    print('x and y are equal')
else:
    if x < y:
        print('x is less than y')
    else:
        print('x is greater than y')

Disney Princess Quiz

How would we approach building a quiz like this?

Process

• Problem Formulation - Conceptualize a problem
• Solution Expression - Formulate unambiguous algorithm
• Execution - Computer runs instructions to produce result
• Evaluation - User explores result to confirm thinking

Star Wars Quiz

age = int(input("How old are you?"))
color = input("What is your favorite color?")

if age < 25:
    if color == 'red':
        print("You are Darth Maul")
    else:
        print("You are Obi-wan Kenobi")
else:
    if color == 'red':
        print("You are Darth Vader")
    else:
        print("You are Luke Skywalker")

Style

• Deep nesting can become difficult to read
• As a rule of thumb, we’d like to avoid nesting more than 3 layers deep
• Lines should not exceed 79 characters (PEP8)

Exit

• exit can be used to immediately terminate a program.

Exit Example

dividend = int(input("Enter value for divdend:"))
divisor = int(input("Enter value for divisor:"))

if divisor == 0:
    print("Can't divide by zero")
    exit()

quotient = dividend // divisor
remainder = dividend % divisor

print("Quotient:", quotient)
print("Remainder:", remainder)

Key Topics to Date

• input and print statements
• Arithmetic expressions (2 + 3)
• Comparison operators (2 <= 3)
• Assignment statements (a=3)
• Conditional execution (if, elif, else)