Sep 03: 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
  • HW2 Reflection on Canvas
• Read Week 3 – ideally:
  • 1st half before Friday
  • 2nd half before Monday
• Submit HW 3 – ideally:
  • 1 and 2 before Friday
  • 3 and 4 before Monday
• Upcoming events
  • CS Dept Club Mixer – Thursday 9/4 at 5:00pm in King 259 + 260
  • Professional Resources – Friday 9/5 at 4:00pm in King Hall 259

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]

Quiz Logistics

Before the quiz:

• Log in to the lab machine as student (no password)
• Open a web browser – do NOT open Thonny until later!
• Log in to Gradescope; close all other tabs and windows
• Silence your phone and place on top of the computer

When the quiz begins:

• Start recording (double click the icon on the desktop)
• Open the "Prac1 Written" assignment on Gradescope
• If you finish early, start reading the coding portion
• You may use the coding portion as scratch paper

At the 10-minute mark:

• Open Thonny when instructed – do NOT open before!
• Test your code in Thonny; Gradescope won't give hints

At the end of the quiz:

• Submit files to Gradescope before the time runs out
• Stop recording when instructed (not when you finish)
• Turn in the coding portion handout to the prof or TA
• Log out as student; you may log back in as yourself

At the end of class:

• Don't forget your phone sitting on the computer
• Do NOT discuss the quiz outside of the classroom

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}.")