Arrays vs Other Data Structures When to Choose Arrays in DSA C++ - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers in C++.

DSA C++

int arr[[1]];

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

A10

Bn

C0

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable like 'n' without defining it.

Using zero as size which creates an empty array.

The array size must be a fixed integer. Here, 5 means the array can hold 5 integers.

2fill in blank

medium

Complete the code to access the third element of the array named 'arr'.

DSA C++

int value = arr[[1]];

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

A2

B3

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 instead of 2 for the third element.

Confusing 1-based indexing with 0-based.

Array indexing starts at 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to correctly initialize an array with values 1, 2, 3.

DSA C++

int arr[3] = { [1] };

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

A1; 2; 3

B1, 2, 3

C1 2 3

D(1, 2, 3)

Attempts:

3 left

💡 Hint

Common Mistakes

Using semicolons instead of commas.

Using parentheses instead of braces.

Array initialization uses commas to separate values inside braces.

4fill in blank

hard

Fill both blanks to create a loop that prints all elements of an array 'arr' of size 'n'.

DSA C++

for (int i = [1]; i [2] n; i++) {
    std::cout << arr[i] << ' ';
}

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

A0

B<=

C<

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting loop at 1, missing the first element.

Using <= which causes out-of-bounds error.

The loop starts at 0 and runs while i is less than n (not less or equal) to avoid out-of-bounds access.

5fill in blank

hard

Fill all three blanks to create a function that returns the sum of elements in an integer array.

DSA C++

int sumArray(int arr[], int n) {
    int sum = 0;
    for (int i = [1]; i [2] n; i[3]) {
        sum += arr[i];
    }
    return sum;
}

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

A0

B<

C++

D--i

Attempts:

3 left

💡 Hint

Common Mistakes

Using --i which decrements and causes infinite loop.

Using <= which causes out-of-bounds.

The loop starts at 0, runs while i is less than n, and increments i by 1 each time.

Practice

1. Which of the following is the best reason to choose an array over other data structures like linked lists or trees?

easy

A. When you need fast access to elements by index

B. When you want to easily insert or delete elements anywhere

C. When you need a flexible size that grows automatically

D. When you want to store key-value pairs

Solution

1. Step 1: Understand array access speed

   Arrays store elements in continuous memory, so accessing by index is very fast (constant time).

2. Step 2: Compare with other structures

   Linked lists and trees have slower access by index because they require traversal.

3. Final Answer:

   When you need fast access to elements by index -> Option A

4. Quick Check:

   Array index access: O(1) [OK]

Hint: Arrays give quick index access, unlike linked lists [OK]

Common Mistakes:

• Thinking arrays allow easy insertion/deletion anywhere
• Confusing arrays with dynamic size structures
• Assuming arrays store key-value pairs

2. Which of the following is the correct way to declare an array of 5 integers in C++?

easy

A. int arr(5);

B. int arr = new int[5];

C. int arr[5];

D. array<int> arr(5);

Solution

1. Step 1: Recall C++ array syntax

   Static arrays in C++ are declared with type, name, and size in square brackets.

2. Step 2: Check each option

   int arr[5]; uses correct syntax: int arr[5];. int arr = new int[5]; is incorrect syntax for static arrays. int arr(5); is invalid for arrays. array<int> arr(5); uses a non-standard syntax.

3. Final Answer:

   int arr[5]; -> Option C

4. Quick Check:

   Static array uses square brackets [OK]

Hint: Use square brackets for static array size in C++ [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Confusing dynamic allocation syntax with static arrays
• Using non-standard array declarations

3. What will be the output of the following C++ code?

int arr[3] = {10, 20, 30};
for (int i = 0; i < 3; i++) {
    std::cout << arr[i] << " ";
}

medium

A. 10 20 30

B. 30 20 10

C. 0 0 0

D. Compilation error

Solution

1. Step 1: Analyze array initialization

   The array arr is initialized with values 10, 20, 30 at indices 0, 1, 2 respectively.

2. Step 2: Trace the loop output

   The loop prints elements from index 0 to 2, so output is "10 20 30 " with spaces.

3. Final Answer:

   10 20 30 -> Option A

4. Quick Check:

   Loop from 0 to < size prints forward [OK]

Hint: Arrays print in stored order unless reversed [OK]

Common Mistakes:

• Assuming reverse order print
• Thinking uninitialized arrays print zeros
• Expecting syntax errors from correct code

4. Identify the error in the following code snippet that uses an array:

int arr[3];
arr[3] = 100;
std::cout << arr[3];

medium

A. Missing semicolon after declaration

B. Array index out of bounds error

C. Syntax error in array declaration

D. No error, code runs fine

Solution

1. Step 1: Check array size and indexing

   The array arr has size 3, so valid indices are 0, 1, 2.

2. Step 2: Identify invalid access

   Accessing arr[3] is out of bounds and causes undefined behavior.

3. Final Answer:

   Array index out of bounds error -> Option B

4. Quick Check:

   Valid indices: 0 <= i < size [OK]

Hint: Array indices start at 0, max index = size-1 [OK]

Common Mistakes:

• Assuming index 3 is valid for size 3 array
• Ignoring runtime errors from invalid access
• Confusing syntax errors with runtime errors

5. You need to store a fixed number of student grades and access them quickly by their position. Which data structure should you choose and why?

medium

A. Linked list, because it allows easy insertion and deletion

B. Binary tree, because it keeps data sorted automatically

C. Hash map, because it stores key-value pairs efficiently

D. Array, because it provides fast index-based access and fixed size

Solution

1. Step 1: Understand the problem requirements

   The number of grades is fixed and access by position (index) should be fast.

2. Step 2: Match data structure properties

   Arrays have fixed size and provide constant time access by index, perfect for this need.

3. Step 3: Compare other options

   Linked lists are slow for index access, hash maps are for key-value pairs, and binary trees are for sorted data.

4. Final Answer:

   Array, because it provides fast index-based access and fixed size -> Option D

5. Quick Check:

   Fast index access + fixed size: array [OK]

Hint: Fixed size + fast access = array choice [OK]

Common Mistakes:

• Choosing linked list for fast index access
• Confusing hash map use case with arrays
• Selecting binary tree without sorting need