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College Board Big Idea 1

Identifying and Correcting Errors (Unit 1.4)

Become familiar with types of errors and strategies for fixing them

  • Review CollegeBoard videos and take notes on blog
  • Complete assigned MCQ questions if applicable

Code Segments

Practice fixing the following code segments!

Segment 1: Alphabet List

Intended behavior: create a list of characters from the string contained in the variable alphabet

Code:

%%js

var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

for (var i = 0; i < 10; i++) {
	alphabetList.push(alphabet[i]);
}

console.log(alphabetList);

<IPython.core.display.Javascript object>

What I Changed

Originally this function printed the a list of numbers from 0-9. Instead I changed the alphabetList.push(i) section to alphabet.push(alphabet[i]) so that instead of printing the numbers, it will bring the letters from variable alphabet. It only takes the letters from 0-9.

Segment 2: Numbered Alphabet

Intended behavior: print the number of a given alphabet letter within the alphabet. For example:

"_" is letter number _ in the alphabet

Where the underscores (_) are replaced with the letter and the position of that letter within the alphabet (e.g. a=1, b=2, etc.)

Code:

%%js

// Copy your previous code to built alphabetList here
var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

let letterNumber = 5

for (var i = 0; i < alphabet.length; i++) {
	if (i === letterNumber) {
		console.log(" e is letter number 5 in the alphabet")
	}
}

// Should output:
// "e" is letter number 5 in the alphabet

<IPython.core.display.Javascript object>

What I Changed

I added the alphabet variable so that ther is no more sytax error and I also changed i < alphabet.length so that 0 is looping the length of the alphabet variable not the alphabetList variable. I also changed the message that is shown if the loop is true so that it prints the correct message.

Segment 3: Odd Numbers

Intended behavior: print a list of all the odd numbers below 10

Code:

%%js

let odds = [];
let i = 1;

while (i <= 10) {
  odds.push(i);
  i += 2;
}

console.log(odds);

<IPython.core.display.Javascript object>

What I Changed

Orginally it prints all of the even numbers between 0 and 10. I changed the variable name to odds because it makes more sense considering we’re trying to print odd numbers. I changed i to be defined as 1 instead of zero so that i when I increment by two it would only show the odd numbers and not the even ones.

BELOW NOT EDITED

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?
  • Make changes to get the intended outcome.
%%js

var numbers = [];
var uniqueNumbers = []; // Array to store unique numbers
var i = 0;

while (i < 100) {
    numbers.push(i);
    i += 1;
}

for (var i of numbers) {
    if (numbers[i] % 5 === 0 && uniqueNumbers.indexOf(numbers[i]) === -1) {
        uniqueNumbers.push(numbers[i]);
    }
    if (numbers[i] % 2 === 0 && uniqueNumbers.indexOf(numbers[i]) === -1) {
        uniqueNumbers.push(numbers[i]);
    }
}

console.log(uniqueNumbers);



<IPython.core.display.Javascript object>

What I Changed

I added an additional array to keep track of the duplicates. Before pushing numbers into the new array (uniqueNumbers) it checks for dupliactes using the indexOf method.

Challenge

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

  • What are some ways to (user) error proof this code?
  • 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.

%%js

var menu =  {"China": 3.99,
         "U.S.A": 1.99,
         "Russia": 0.99}
var total = 0

//shows the user the menu and prompts them to select an item
console.log("Menu")
for (var item in menu) {
    console.log(item + "  $" + menu[item].toFixed(2)) //why is toFixed used?
}
//ideally the code should support mutliple items
var item = "China"

//code should add the price of the menu items selected by the user 
console.log(total)

Hacks

  • Fix the errors in the first three segments in this notebook and say what you changed in the code cell under “What I Changed” (Challenge is optional)