CS 111 f21 — Functions and Conditionals part 3

Table of Contents

1 Practice

  • Write an average_grade function that takes three numeric grades as parameters and returns their average1
  • Function mysteries

    • What will be printed?2 

      def f(x):
    return x + 2
def g(y):
    return y * 3
a = 2
print(f(g(a)), g(f(a)))

    • What will be printed?3 

      def f(x):
    return x + 2
def g(y):
    return f(y) * f(y + 1)
a = 2
print(g(a))
  • Write an absolute value function: takes one number as a parameter, returns the positive version of that number (hint: if x is negative, -x is the positive version).4

  • What will be printed?5 

    def km_to_miles(km):
    miles = km * 1.61
    print(miles)
running = 10
if km_to_miles(running) < 26.2:
    print("not a marathon")
  • Given a player's guess and a secret number, print "cold" "warm" or "lava" (or "WINNER" if the guess is correct)6
    • Assume you have a variable guess with the player's guess and a variable secret with the secret number
    • Up to you to choose how close "lava" is, etc.
    • Make sure to only print one hint

2 User Input

  • built-in input function, takes a string argument to use as the prompt 

    name = input("What is your name? ")
  • input returns a string (text), so if we need it as a number (e.g., a player guessing a number), we have to convert it
  • Python distinguishes between integers (whole numbers) and floating point (real or decimal numbers)
    • Why? The computer has to represent and interact with these two types of data very differently
    • Take CS 208 to find out more!
  • Named int and float in Python
  • float can be treacherous!
    • (2.5*0.1)*1.5 == 2.5*(0.1*1.5) is False
    • 0.1*1.5*2.5 == 2.5*0.1*1.5 is False
    • computer can only approximate

  • We can use the built-in functions int and float to convert text to a number: 

    guess = int(input("Enter your guess: "))

3 Randomness

  • As you've seen in Lab 1, use Python's random module
    • pseudo-random number generator (deterministic, repeats eventually)
    • series of numbers based on initial seed
    • will eventually repeat: period of \(2^{19937}-1\)

  • To get a random number between lowest and highest: 

    import random
number = random.randint(lowest, highest)

Footnotes:

1 
def average_grade(grade1, grade2, grade3):
    return (grade1 + grade2 + grade3) / 3
2

8 12

3

20

4 
def abs(x):
    if x < 0:
        return -x
    else:
        return x
5

It will print 16.1 and then encounter a TypeError

6 
difference = abs(secret - guess)
if difference == 0:
    print("WINNER")
elif difference < 5:
    print("lava")
elif difference < 10:
    print("warm")
else:
    print("cold")