Week 5 - Problem solving methods

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Week 5 Assignment

Task 1

Count values above a threshold

You are given an array of numbers and a threshold value.

Write a function that returns how many numbers in the array are greater than the threshold.

Function Signature

function countAboveThreshold(numbers, threshold) {
  // Your code here
}

Requirements

• Return the count of numbers greater than the threshold
• If the array is empty, return 0
• Assume the input is valid

Example Usage

countAboveThreshold([1,5,10,3],4)// returns 2
countAboveThreshold([7,8,9],10)// returns 0
countAboveThreshold([],5)// returns 0

Task 2

Write Unit Tests

Your task is to write unit tests for the function below using Vitest.

You must not change the function implementation.

Your job is to prove that it works correctly by writing meaningful test cases.

Function to Test

export function calculateAverage(numbers) {
  if (!Array.isArray(numbers)) {
    return null;
  }

  if (numbers.length === 0) {
    return null;
  }

  let sum = 0;

  for (const num of numbers) {
    if (typeof num !== "number") {
      return null;
    }
    sum += num;
  }

  return sum / numbers.length;
}

What the Function Does

• Returns the average of numbers in an array
• Returns null if:
  • the input is not an array
  • the array is empty
  • the array contains a non-number value

Requirements

Your unit tests should:

• Use Vitest
• Test the function without modifying it
• Clearly describe what each test is checking
• Cover both valid and invalid inputs

Test Cases to Include

Make sure your tests cover at least the following scenarios:

1. A normal case with valid numbers
   • Example: [2, 4, 6] → 4
2. An array with a single number
   • Example: [5] → 5
3. An empty array
   • Expected result: null
4. A non-array input
   • Example: "123" or null → null
5. An array containing a non-number value
   • Example: [1, 2, "3"] → null

Expected Outcome

By the end of this task, your test file should clearly demonstrate that:

• The function works correctly for valid input
• The function safely handles invalid input

Task 3

Debug and Fix the Logic

In this task, you will practice finding and fixing errors by debugging. The code below runs, but it does not behave as expected.

Problem

The function below is supposed to return the number of vowels in a string.

Function to Debug

function countVowels(text) {
  let count = 0;

  for (let i = 0; i <= text.length; i++) {
    if (
      text[i] === "a" ||
      text[i] === "e" ||
      text[i] === "i" ||
      text[i] === "o" ||
      text[i] === "u"
    ) {
      count++;
    }
  }

  return count;
}

Your Task

1. Run the function with different inputs.
2. Use the debugger to observe:
   • the value of i
   • the value of text[i]
   • when count increases
3. Identify what is wrong with the logic.
4. Fix the function so it works correctly.

Example Usage

countVowels("hello")// returns 2
countVowels("javascript")// returns 3
countVowels("")// returns 0

Things to think about

• What happens in the last loop iteration?
• What value does text[i] have when i === text.length?
• Should uppercase vowels be counted?

Expected Outcome