Computer Programming 2020/21 spring

Homework for Week 3

Conditional execution

Watch the videos about how Python executes some statements and skips others:

Quiz

Go to Moodle and solve the third quiz about video lectures. You can solve the quiz several times, best attempt counts.

Examples

This week we are into if-else and try-except statements. In real world, programs are developed by mixing these construcs (and others that we'll learn in the future). For example, you can write a program that asks for an input, checks if it is valid, and depending on value entered, chooses what to output.

Example 1

age_as_string = input("How old are you? ")
try:
    # Try to convert the input to an integer
    age = int(age_as_string)
except:
    # Conversion failed, let age be -1 in this case
    age = -1

if age < 0:
    print("This is not a valid age")
elif age < 18:
    print("You are a minor")
elif age < 100:
    print("You are an adult")
else:
    print("Wow, you need a lot of birthday candles!")

Example 2

try:
    x = int(input('Enter the first number: '))
    y = int(input('Enter the second number: '))
except:
    print('Please enter a number')
else:
    # If both int coversions were successful, then continue here
    if x == y:
        print('Numbers are equal')
    else:
        if x < y:
            print(x, 'is less than', y)
        else:
            print(x, 'is greater than', y)

Exercises

1. Speeding fine

When the maximum driving speed is exceeded, a fine is imposed. The size of the fine is obtained by multiplying the number of km/h's above the allowed limit by 3. The maximum fine is 190 euros.

Write a program that

• prompts the user for the name, speed limit, and actual speed;
• calculates the fine according to the rules above;
• outputs the name and the size of the fine on the screen.

Example

 Enter name: Jürgen
 Enter speed limit (km/h): 60
 Enter actual speed (km/h): 80

 Jürgen, your fine for speeding is €60.

Explanation: the speed limit is exceeded by 80 − 60 = 20 km/h. Therefore, the fine is 3 · 20 = 60 euros.

Second example

 Enter name: Hendrik
 Enter speed limit (km/h): 50
 Enter actual speed (km/h): 172

 Hendrik, your fine for speeding is €190.

Explanation: the speed is exceeded by 172 − 50 = 122 km/h. The calculation gives a fine of 3 · 122 = 366 euros. Since it exceeds the maximum amount of the fine, the actual fine will be 190 euros.

2. Tax-free income

The amount of tax-free income in Estonia currently depends on the annual income:

• for annual income up to 6000 euros, tax-free income is equal to annual income
• for annual income from 6000 euros to 14400 euros, tax-free income is 6000 euros
• for annual income from 14400 euros to 25200 euros, tax-free income is computed according to the formula 6000 – 6000 ÷ 10800 × (annual_income – 14400)
• for annual income over 25200 euros, tax-free income is 0 euros.

Write a program that asks for user's annual income (nonnegative floating point number) and computes and outputs the tax-free income rounded to two decimal places.

If the user enters a non-numeric value as the annual income, then the program prints a corresponding message (use try-except). Also the program prints a message, if the user enters a negative value as the annual income.

Example

 Enter your annual income: 16825
 Your tax-free income is 4652.78 euros

 Enter your annual income: large
 Please enter a number!

 Enter your annual income: -100
 Please enter a non-negative value!

Hint

>>> round(16.6333, 2)
16.63

Submit your solutions

Submit your solutions of exercises 1 and 2 to the autograder in Moodle, under Homework for Week 3.

NB! Use home1.py and home2.py as the names of your files.