Identifying and Correcting Errors (Unit 1.4)

Become familiar with types of errors and strategies to fixing them

Lightly Review Videos and take notes on topics with Blog

Complete assigned MCQ questions

Here are some code segments you can practice fixing:

alphabet = "abcdefghijklmnopqrstuvwxyz"

alphabetList = []

for i in alphabet:
    alphabetList.append(i)

print(alphabetList)

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

The intended outcome is to determine where the letter is in the alphabet using a while loop

What is a good test case to check the current outcome? Why?
- A or C because it is easy for the user to correctly identify their position.
Make changes to get the intended outcome.

letter = input("What letter would you like to check?")

i = 0

while i < 26:
    if alphabetList[i] == letter:
        print("The letter " + letter + " is the " + str(i+1) + " letter in the alphabet")
    i += 1

The letter a is the 1 letter in the alphabet

The intended outcome is to determine where the letter is in the alphabet using a for loop

What is a good test case to check the current outcome? Why?
- A, B, or Z because their position is commonly known.
Make changes to get the intended outcome.

letter = input("What letter would you like to check?")

count = 1

for i in alphabetList:
    if i == letter:
        print("The letter " + letter + " is the " + str(count) + " letter in the alphabet")
    count += 1

The letter z is the 26 letter in the alphabet

This code outputs the even numbers from 0 - 10 using a while loop.

Analyze this code to determine what can be changed to get the outcome to be odd numbers. (Code block below)
- Change initial value of i to an odd number

evens = []
i = 1

while i <= 10:
    evens.append(i)
    i += 2

print(evens)

[1, 3, 5, 7, 9]

This code should output the odd numbers from 0 - 10 using a while loop.

odds = []
i = 1

while i <= 10:
    odds.append(i)
    i += 2

print(odds)

[1, 3, 5, 7, 9]

This code outputs the even numbers from 0 - 10 using a for loop.

Analyze this code to determine what can be changed to get the outcome to be odd numbers. (Code block below)
- change remainder to 1

numbers = [0,1,2,3,4,5,6,7,8,9,10]
evens = []

for i in numbers:
    if (numbers[i] % 2 == 1):
        evens.append(numbers[i])

print(evens)

[1, 3, 5, 7, 9]

This code should output the odd numbers from 0 - 10 using a for loop.

numbers = [0,1,2,3,4,5,6,7,8,9,10]
odds = []

for i in numbers:
    if (numbers[i] % 2 == 1):
        odds.append(numbers[i])

print(odds)

[1, 3, 5, 7, 9]

The intended outcome is printing a number between 1 and 100 once, if it is a multiple of 2 or 5

What values are outputted incorrectly. Why?
- Every multiple of 10 is duplicated in the place of the next value.
Make changes to get the intended outcome.

numbers = []
newNumbers = []
i = 0

while i <= 100:
    numbers.append(i)
    i += 1

for i in range(1, 101):
    if numbers[i] % 5 == 0:
        newNumbers.append(numbers[i])
    elif numbers[i] % 2 == 0:
        newNumbers.append(numbers[i])

print(newNumbers)

[2, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, 52, 54, 55, 56, 58, 60, 62, 64, 65, 66, 68, 70, 72, 74, 75, 76, 78, 80, 82, 84, 85, 86, 88, 90, 92, 94, 95, 96, 98, 100]

Challenge

This code segment is at a very early stage of implementation.

What are some ways to (user) error proof this code?
- Execute the code and work through any bugs
The code should be able to calculate the cost of the meal of the user

Hint:

write a “single” test describing an expectation of the program of the program
test - input burger, expect output of burger price
run the test, which should fail because the program lacks that feature
write “just enough” code, the simplest possible, to make the test pass

Then repeat this process until you get program working like you want it to work.

menu =  {"burger": 3.99,
         "fries": 1.99,
         "drink": 0.99}
total = 0

#shows the user the menu and prompts them to select an item
print("Menu")
for k,v in menu.items():
    print(k + "  $" + str(v)) #why does v have "str" in front of it?

#ideally the code should prompt the user multiple times
item = input("Please select an item from the menu, or click enter if you are done.")

full = 0

j = []

while item != "":
    j.append(item)
    item = input("Please select an item from the menu, or click enter if you are done.")

for item in j:
    if item in menu.keys():
        full = full + menu[item]




#code should add the price of the menu items selected by the user 
print(round(full, 3))

Menu
burger  $3.99
fries  $1.99
drink  $0.99
6.97

AP Classroom Video Notes

For errors in an algorithm or program:
- Identify the error
  - Logic error
    - mistake in algorithm or program that causes it to behave incorrectly or unexpectedly
  - Syntax error
    - A mistake where the rules of the programming language are not followed
  - run-time error
    - Occurs during execution of program
    - Programming languages define their own runtime errors
  - Overflow error
    - Error that occurs when a computer attempts to handle a number that is outside of the defined range of values
- Correct errors
  - test cases
    - testing certain inputs to figure out what is wrong with the program
  - Border cases
    - testing inputs that are likely to mess up in the program
  - hand tracing
    - Writing out the values of the variable within the loop as it iterates to determine if the outcome is correct
    - Really only useful for small code segments that iterate a small number of times
  - visualizations
  - debuggers
  - adding extra output statement(s)
    - Helps programmers determine where an error is in a program
Programmers constantly run into errors when writing programs
- They expect to encounter errors and are prepared to resolve them
Testing
- uses defined inputs to ensure that an algorithm or program is producing the expected outcome(s)
  - Programmers use the results from testing to revise their algorithms or programs
  - Defined inputs should demonstrate the different expected outcomes that are at or just beyond the extremes of input data
  - Program requirements are needed to identify appropriate defined inputs for testing

Hacks

Now is a good time to think about Testing of your teams final project...

What errors may arise in your project?

misdirection/confusion of pages

What are some test cases that can be used?

Corner cases

Make sure to document any bugs you encounter and how you solved the problem.

Okay.

What are “single” tests that you will perform on your project? Or, your part of the project?

As Hack Design and Test plan action … Divide these “single” tests into Issues for Scrum Board prior to coding. FYI, related tests could be in same Issue by using markdown checkboxes to separate tests.