Why Arrays Exist and What Problem They Solve in DSA C++ - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

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

DSA C++

int numbers[[1]];

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

A0

B5

C10

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or a variable without initialization as size.

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

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 instead of 2 for the third element index.

Array indexing in C++ 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'

A(1, 2, 3)

B1 2 3

C1; 2; 3

D1, 2, 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces or semicolons instead of commas.

Array initialization requires comma-separated values inside braces.

4fill in blank

hard

Fill both blanks to create an array of size 4 and assign 10 to its first element.

DSA C++

int arr[[1]];
arr[[2]] = 10;

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

A4

B0

C1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first element index.

The array size is 4, and the first element index is 0.

5fill in blank

hard

Fill all three blanks to declare an array, assign a value, and print the second element.

DSA C++

#include <iostream>
int main() {
    int arr[[1]] = {5, 10, 15};
    arr[[2]] = 20;
    std::cout << arr[[3]] << std::endl;
    return 0;
}

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

A3

B1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing element positions with indices.

The array size is 3, the second element index is 1, and printing the third element uses index 2.

Practice

1. Why do arrays exist in programming languages like C++?

easy

A. To store multiple values of the same type in a single variable

B. To perform mathematical calculations faster

C. To create functions that run automatically

D. To store different types of data in one place

Solution

1. Step 1: Understand the purpose of arrays

   Arrays are designed to hold many values of the same type together, making it easier to manage related data.

2. Step 2: Compare options with array purpose

   Only To store multiple values of the same type in a single variable correctly describes this purpose. Other options describe unrelated features.

3. Final Answer:

   To store multiple values of the same type in a single variable -> Option A

4. Quick Check:

   Arrays store same-type values together = B [OK]

Hint: Arrays group same-type data in one variable [OK]

Common Mistakes:

• Thinking arrays store different data types
• Confusing arrays with functions
• Believing arrays speed up all calculations

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

easy

A. int arr = new int[5];

B. array int arr(5);

C. int arr[5];

D. int arr{5};

Solution

1. Step 1: Recall C++ array declaration syntax

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

2. Step 2: Check each option

   int arr[5]; matches correct syntax. array int arr(5); is invalid syntax. int arr = new int[5]; uses dynamic allocation incorrectly without pointer. int arr{5}; is list initialization, not array declaration.

3. Final Answer:

   int arr[5]; -> Option C

4. Quick Check:

   C++ array syntax = int name[size]; [OK]

Hint: Use type name[size] to declare arrays in C++ [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing dynamic allocation with static arrays
• Using curly braces for array size

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. Compilation error

B. 0 0 0

C. 10 20 30 0

D. 10 20 30

Solution

1. Step 1: Analyze array initialization

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

2. Step 2: Trace the for loop output

   The loop prints each element followed by a space: 10, then 20, then 30.

3. Final Answer:

   10 20 30 -> Option D

4. Quick Check:

   Print all initialized array elements = D [OK]

Hint: Loop prints each array element in order [OK]

Common Mistakes:

• Assuming uninitialized values print zero
• Expecting extra zero at end
• Thinking code won't compile

4. Identify the error in this C++ code snippet:

int arr[3];
arr[3] = 100;
std::cout << 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: Identify invalid index usage

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

3. Final Answer:

   Array index out of bounds error -> Option A

4. Quick Check:

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

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

Common Mistakes:

• Using index equal to array size
• Thinking arrays start at 1
• Ignoring runtime errors from invalid access

5. You want to store the daily temperatures for a week and calculate their average. Why is using an array a good choice here?

hard

A. Because arrays automatically calculate averages

B. Because arrays allow storing multiple related values with easy access by index

C. Because arrays can store different data types together

D. Because arrays grow dynamically as you add values

Solution

1. Step 1: Understand the problem requirements

   You need to store multiple temperature values for each day and access them easily to calculate average.

2. Step 2: Match array features to the problem

   Arrays store multiple values of the same type in order and allow access by index, perfect for daily temperatures.

3. Final Answer:

   Because arrays allow storing multiple related values with easy access by index -> Option B

4. Quick Check:

   Arrays store related data with index access = A [OK]

Hint: Use arrays to hold related data accessed by position [OK]

Common Mistakes:

• Thinking arrays calculate values automatically
• Believing arrays store mixed data types
• Assuming arrays resize automatically