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.

DSA C

int numbers[[1]];

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

A10

B0

C5

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative numbers as size

Forgetting the size inside brackets

The number inside the brackets specifies the size of the array. 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 'data'.

DSA C

int value = data[[1]];

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

A0

B3

C1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 instead of 2 for the third element

Confusing 1-based indexing

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

D1; 2; 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using semicolons instead of commas

Missing commas between values

Array initialization requires commas between values inside braces.

4fill in blank

hard

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

DSA C

for (int i = [1]; i [2] n; i++) {
    printf("%d\n", 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

Using <= which causes out-of-bounds access

The loop starts at 0 because array indices start at 0. The condition uses < because the last valid index is n-1.

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

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

Asize

B<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causing out-of-bounds

Not passing array size as parameter

The function takes the array size as 'size'. The loop runs while i < size to avoid out-of-bounds access.

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 changes often

D. When you want to store key-value pairs

Solution

1. Step 1: Understand array access

   Arrays store elements in contiguous 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. Arrays are best for fast index access.

3. Final Answer:

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

4. Quick Check:

   Fast index access = B [OK]

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

Common Mistakes:

• Thinking arrays are best for frequent insertions/deletions
• Confusing arrays with key-value stores
• Assuming arrays resize automatically

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

easy

A. int arr = new int[5];

B. int arr[5];

C. int arr();

D. array<int> arr(5);

Solution

1. Step 1: Recall C array syntax

   In C, arrays are declared with the type, name, and size in square brackets, like int arr[5];.

2. Step 2: Check other options

   int arr(); uses parentheses which is a function declaration. int arr = new int[5]; is C++ style with new. array<int> arr(5); is not valid C syntax.

3. Final Answer:

   int arr[5]; -> Option B

4. Quick Check:

   C arrays use square brackets for size = C [OK]

Hint: C arrays use square brackets for size declaration [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using C++ style new keyword in C
• Confusing array declaration with function declaration

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

int arr[3] = {10, 20, 30};
printf("%d", arr[1]);

medium

A. 10

B. Compilation error

C. 20

D. 30

Solution

1. Step 1: Understand array initialization

   The array arr has elements 10 at index 0, 20 at index 1, and 30 at index 2.

2. Step 2: Identify printed element

   The code prints arr[1], which is the second element, value 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Array indexing starts at 0, so arr[1] is second element [OK]

Common Mistakes:

• Confusing index 1 with first element
• Expecting compilation error due to syntax
• Mixing up array initialization order

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

int arr[3];
arr[3] = 100;
printf("%d", arr[3]);

medium

A. Array index out of bounds error

B. Syntax error in array declaration

C. Missing semicolon after 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, and 2.

2. Step 2: Analyze the assignment and print

   The code assigns and prints arr[3], which is outside the valid range, causing out of bounds access.

3. Final Answer:

   Array index out of bounds error -> Option A

4. Quick Check:

   Index 3 invalid for size 3 array = A [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Assuming index 3 is valid for size 3 array
• Thinking syntax error due to semicolon
• Believing code runs without error

5. You need to store a fixed number of sensor readings that will not change in size and require fast access by position. Which data structure is the best choice and why?

hard

A. Binary tree, because it keeps data sorted automatically

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

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

D. Array, because it provides fast indexed access and fixed size

Solution

1. Step 1: Analyze requirements

   The sensor readings count is fixed and will not change, and fast access by position is needed.

2. Step 2: Match data structure features

   Arrays have fixed size and allow fast access by index. Linked lists are slower for access. Hash tables and trees serve different purposes.

3. Final Answer:

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

4. Quick Check:

   Fixed size + fast access = Array = A [OK]

Hint: Fixed size and fast access? Choose array [OK]

Common Mistakes:

• Choosing linked list for fixed size data
• Confusing hash table use case
• Thinking binary tree is best for fixed size arrays