Sep 04: Prac1, if-else Statements

Learning Objectives

After today's class, you should be able to:

• Explain the logistics for taking a quiz in CS 149.
• Describe the behavior of if, elif, and else.

Reminders

• Due TODAY
  • TeamPref on Canvas
  • Tip: Look at 1Pic1Par
  • HW2 Reflection on Canvas
• Upcoming events
  • CS Dept Club Mixer 9/5
  • First Year Kickoff 9/11
• Read Ch 3 – ideally:
  • 1st half before Friday
  • 2nd half before Monday
• Submit HW 3 – ideally:
  • 1 and 2 before Friday
  • 3 and 4 before Monday

HW2 Debrief

[10 min]

Some highlights:

• Splitting up long lines of code
• Rounding to n decimal places
• Using math module functions
• // and % usually go together

Practice Quiz 1

[25 min]

Instructions:

• Log in as student
• Only two windows:
  1. Thonny
  2. Web browser
• Web traffic monitored
• Log out when finished

Ch03 Preview

[15 min]

• Keywords: if, elif ("else if"), else
• == is a comparison operator ("is equal to")
  • = is the assignment operator ("is now")
• Indented blocks show the program structure
  • The line before always ends with a colon
• Demo: Stepping over code with the debugger
  • Go to Tools > Options… > Run & Debug
  • Change preferred debugger to "faster"

import math

print("Welcome to the fraction reducer!")

# Input the fraction as two integers
print()
numer = int(input("Numerator? "))
denom = int(input("Denominator? "))
print()

if denom == 0:
    print("Sorry, you can't divide by 0")
    print("Have a nice day")
else:
    # Divide by the greatest common divisor
    gcd = math.gcd(numer, denom)
    numer2 = numer // gcd
    denom2 = denom // gcd

    # Output the result in the right format
    if denom2 == 1:
        print(f"{numer}/{denom} reduces to {numer2}.")
    elif denom2 == denom:
        print(f"{numer}/{denom} is already reduced!")
    else:
        print(f"{numer}/{denom} reduces to {numer2}/{denom2}.")