Array Access and Update at Index in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the element at index 2 in the array.

DSA Typescript

const arr = [10, 20, 30, 40];
const value = arr[[1]];
console.log(value);

Drag options to blanks, or click blank then click option'

A2

B3

C1

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 to access the third element (off by one error).

Using index 4 which is out of bounds.

Index 2 accesses the third element in the array, which is 30.

2fill in blank

medium

Complete the code to update the element at index 1 to 50.

DSA Typescript

const arr = [10, 20, 30];
arr[[1]] = 50;
console.log(arr);

Drag options to blanks, or click blank then click option'

A2

B1

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Updating index 0 instead of 1.

Using index 3 which is out of bounds.

Index 1 refers to the second element, which is updated to 50.

3fill in blank

hard

Fix the error in the code to correctly update the last element to 100.

DSA Typescript

const arr = [5, 10, 15];
arr[[1]] = 100;
console.log(arr);

Drag options to blanks, or click blank then click option'

A-1

B3

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 which is out of bounds.

Using negative index which is not valid in TypeScript.

Index 2 is the last element in the array of length 3.

4fill in blank

hard

Fill both blanks to access and update the element at index 0 to 99.

DSA Typescript

const arr = [1, 2, 3];
arr[[1]] = [2];
console.log(arr);

Drag options to blanks, or click blank then click option'

A0

B99

C1

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong index like 1 or 3.

Assigning wrong value like 100 instead of 99.

Index 0 accesses the first element, which is updated to 99.

5fill in blank

hard

Fill all three blanks to double the value at index 2 and update it.

DSA Typescript

const arr = [2, 4, 6];
arr[[1]] = arr[[2]] [3] 2;
console.log(arr);

Drag options to blanks, or click blank then click option'

A2

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using different indexes for BLANK_1 and BLANK_2.

Using addition instead of multiplication.

Index 2 accesses the third element; multiplying by 2 doubles it.

Practice

1. What does the expression arr[2] do in an array arr?

easy

A. Accesses the element at index 2 of the array

B. Adds a new element at index 2

C. Removes the element at index 2

D. Returns the length of the array

Solution

1. Step 1: Understand array indexing

   Arrays use zero-based indexing, so index 2 means the third element.

2. Step 2: Access element at index 2

   The expression arr[2] retrieves the element stored at the third position.

3. Final Answer:

   Accesses the element at index 2 of the array -> Option A

4. Quick Check:

   arr[2] means get element at index 2 [OK]

Hint: Remember arrays start at 0, so index 2 is third element [OK]

Common Mistakes:

• Thinking index 2 adds or removes elements
• Confusing index with length
• Assuming indexing starts at 1

2. Which of the following is the correct way to update the element at index 1 in a TypeScript array nums to 10?

easy

A. nums.add(1, 10);

B. nums.update(1, 10);

C. nums.set(1, 10);

D. nums[1] = 10;

Solution

1. Step 1: Recall array element update syntax

   In TypeScript, to update an element at a specific index, use array[index] = value;.

2. Step 2: Apply to given array

   So, nums[1] = 10; correctly updates the element at index 1 to 10.

3. Final Answer:

   nums[1] = 10; -> Option D

4. Quick Check:

   Use bracket notation with assignment for update [OK]

Hint: Use bracket and equals sign to update array element [OK]

Common Mistakes:

• Using non-existent methods like update(), set(), add()
• Confusing update syntax with other languages
• Trying to use push() to update element

3. What will be the output of the following TypeScript code?

const arr = [5, 10, 15];
arr[1] = 20;
console.log(arr);

medium

A. [5, 10, 15]

B. [20, 10, 15]

C. [5, 20, 15]

D. [5, 15, 20]

Solution

1. Step 1: Analyze initial array and update

   The array starts as [5, 10, 15]. The statement arr[1] = 20; changes the element at index 1 from 10 to 20.

2. Step 2: Determine final array state

   After update, the array becomes [5, 20, 15]. The console.log prints this updated array.

3. Final Answer:

   [5, 20, 15] -> Option C

4. Quick Check:

   Update index 1 to 20 changes array to [5, 20, 15] [OK]

Hint: Remember index 1 is second element, update it directly [OK]

Common Mistakes:

• Not updating the element, so output stays same
• Mixing up indexes and values
• Assuming update changes order

4. Identify the error in the following TypeScript code that tries to update an array element:

let fruits = ['apple', 'banana', 'cherry'];
fruits(1) = 'orange';

medium

A. Using parentheses instead of square brackets for indexing

B. Array is declared with let instead of const

C. Missing semicolon at the end of the line

D. Trying to assign a string to an array element

Solution

1. Step 1: Check array element update syntax

   Array elements must be accessed or updated using square brackets [], not parentheses ().

2. Step 2: Identify the error in code

   The code uses fruits(1) = 'orange'; which is invalid syntax. It should be fruits[1] = 'orange';.

3. Final Answer:

   Using parentheses instead of square brackets for indexing -> Option A

4. Quick Check:

   Use square brackets [] to access/update array elements [OK]

Hint: Use [] not () to access or update array elements [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Thinking let vs const causes error here
• Ignoring syntax errors due to missing semicolon

5. Given the array let scores = [10, 20, 30, 40, 50];, which code snippet correctly doubles the value at index 3 and then prints the updated array?

hard

A. scores[3] = scores[3] * 2;
console.log(scores);

B. scores[3] *= 2;
console.log(scores);

C. scores.update(3, scores[3] * 2);
console.log(scores);

D. scores[3] = scores[3] + scores[3];
console.log(scores);

Solution

1. Step 1: Understand how to double element at index 3

   Index 3 corresponds to the fourth element (value 40). Doubling means multiplying by 2.

2. Step 2: Check each option for correct syntax and effect

   scores[3] = scores[3] * 2; console.log(scores); uses explicit multiplication and assignment, which works. scores[3] *= 2; console.log(scores); uses shorthand *= operator, also correct. scores.update(3, scores[3] * 2); console.log(scores); uses a non-existent method update(). scores[3] = scores[3] + scores[3]; console.log(scores); adds the element to itself, which also doubles it.

3. Step 3: Identify the best concise and correct option

   scores[3] *= 2; console.log(scores); is the most concise and idiomatic way to double the value at index 3.

4. Final Answer:

   scores[3] *= 2; console.log(scores); -> Option B

5. Quick Check:

   Use *= operator to double value at index 3 [OK]

Hint: Use *= operator to multiply and update in one step [OK]

Common Mistakes:

• Using non-existent update() method
• Forgetting to print the array after update
• Using addition instead of multiplication