Multi-dimensional arrays in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a 2D array of integers with 3 rows and 4 columns.

C++

int arr[3][[1]];

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

A5

B3

C4

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing rows and columns sizes.

Using the wrong number for the second dimension.

The second dimension size is the number of columns, which is 4 here.

2fill in blank

medium

Complete the code to access the element in the second row and third column of a 2D array named 'matrix'.

C++

int value = matrix[[1]][2];

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

A1

B2

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 1 for the second row index.

Confusing row and column indices.

Array indices start at 0, so the second row is index 1.

3fill in blank

hard

Fix the error in the code to correctly initialize a 2D array with 2 rows and 3 columns.

C++

int grid[2][3] = {{ {1, 2, 3}, [1] }};

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

A{4, 5, 6}

B(4, 5, 6)

C[4, 5, 6]

D4, 5, 6

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets or parentheses instead of curly braces.

Not enclosing the second row in braces.

Each row must be enclosed in braces {}. So the second row is {4, 5, 6}.

4fill in blank

hard

Fill both blanks to declare and initialize a 2D array named 'table' with 2 rows and 2 columns, containing values 1, 2, 3, 4.

C++

int table[[1]][[2]] = {{ {1, 2}, {3, 4} }};

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

A2

B3

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 or 4 instead of 2 for dimensions.

Mixing up rows and columns.

The array has 2 rows and 2 columns, so both dimensions are 2.

5fill in blank

hard

Fill all three blanks to create a nested loop that prints all elements of a 2D array 'data' with 3 rows and 2 columns.

C++

for (int i = 0; i < [1]; i++) {
    for (int j = 0; j < [2]; j++) {
        std::cout << data[i][j] << [3];
    }
    std::cout << std::endl;
}

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

A3

B2

C" "

D"\n"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loop limits.

Printing newline inside inner loop instead of space.

The outer loop runs 3 times for rows, inner loop 2 times for columns, and elements are separated by a space.

Practice

1. What is a multi-dimensional array in C++?

easy

A. A variable that holds a single number

B. An array that stores only one value

C. A function that returns multiple values

D. An array with more than one index, like rows and columns

Solution

1. Step 1: Understand array dimensions

   A multi-dimensional array uses multiple indexes to access elements, such as row and column in a table.

2. Step 2: Compare options

   Only An array with more than one index, like rows and columns describes an array with more than one index, matching the concept of multi-dimensional arrays.

3. Final Answer:

   An array with more than one index, like rows and columns -> Option D

4. Quick Check:

   Multi-dimensional array = multiple indexes [OK]

Hint: Think of rows and columns in a table for multi-dimensional arrays [OK]

Common Mistakes:

• Confusing arrays with single values
• Thinking functions return multiple values
• Mixing variables with arrays

2. Which of the following is the correct way to declare a 2D array of integers with 3 rows and 4 columns in C++?

easy

A. int arr[3][4];

B. int arr(3,4);

C. int arr[4][3];

D. int arr{3,4};

Solution

1. Step 1: Recall C++ 2D array syntax

   The correct syntax uses square brackets with sizes: int arr[rows][columns];

2. Step 2: Check each option

   int arr[3][4]; uses int arr[3][4]; which means 3 rows and 4 columns, correct syntax. Others are invalid or reversed.

3. Final Answer:

   int arr[3][4]; -> Option A

4. Quick Check:

   Use square brackets for dimensions [OK]

Hint: Use square brackets for rows and columns in declaration [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Swapping row and column sizes
• Using curly braces for declaration

3. What is the output of the following C++ code?

int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
std::cout << arr[1][2];

medium

A. 6

B. 3

C. 4

D. 2

Solution

1. Step 1: Understand array initialization

   The array has 2 rows and 3 columns: first row {1,2,3}, second row {4,5,6}.

2. Step 2: Access element arr[1][2]

   Row index 1 is second row, column index 2 is third element: value is 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   arr[1][2] = 6 [OK]

Hint: Remember indexes start at 0; arr[1][2] is second row, third column [OK]

Common Mistakes:

• Confusing row and column indexes
• Forgetting zero-based indexing
• Reading wrong element from array

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

int matrix[2][2] = {{1, 2}, {3}};
std::cout << matrix[1][1];

medium

A. Missing value in second row initialization

B. Array size mismatch causes compile error

C. No error, code runs and prints 0

D. Incorrect use of std::cout syntax

Solution

1. Step 1: Check array initialization

   The second row has only one value {3}, missing one element for 2 columns.

2. Step 2: Understand C++ behavior for missing elements

   Missing elements are initialized to 0 automatically, so matrix[1][1] is 0.

3. Step 3: Check output statement

   std::cout syntax is correct, so it prints 0 without error.

4. Final Answer:

   No error, code runs and prints 0 -> Option C

5. Quick Check:

   Missing elements default to 0 in arrays [OK]

Hint: Missing elements in array init become zero, no error [OK]

Common Mistakes:

• Assuming missing elements cause errors
• Thinking std::cout syntax is wrong
• Expecting garbage values instead of zero

5. How can you sum all elements of a 3x3 integer array named grid in C++?

hard

A. Use std::accumulate directly on the 2D array

B. Use nested loops to add each element to a sum variable

C. Use a single loop from 0 to 8 to sum elements

D. Add only the first row elements

Solution

1. Step 1: Understand 2D array traversal

   To access all elements in a 3x3 array, use two loops: one for rows, one for columns.

2. Step 2: Sum elements with nested loops

   Inside inner loop, add each element grid[i][j] to a sum variable to get total sum.

3. Final Answer:

   Use nested loops to add each element to a sum variable -> Option B

4. Quick Check:

   Nested loops sum all elements [OK]

Hint: Use two loops: outer for rows, inner for columns [OK]

Common Mistakes:

• Using single loop ignoring 2D structure
• Summing only part of the array
• Trying to use std::accumulate on 2D array directly