Multi-dimensional arrays in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested loop accessing 2D array

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

C++

#include <iostream>
int main() {
    int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            std::cout << arr[i][j] << " ";
        }
    }
    return 0;
}

A 1 4 2 5 3 6

B 1 2 3 4 5 6

C 6 5 4 3 2 1

D 1 2 3 6 5 4

💡 Hint

Think about how the nested loops iterate rows then columns.

The outer loop goes through rows (0 and 1), and the inner loop goes through columns (0 to 2). So it prints all elements in row 0, then all in row 1.

❓ Predict Output

intermediate

Value of element after assignment in 3D array

What is the value of arr[1][0][2] after running this code?

C++

#include <iostream>
int main() {
    int arr[2][2][3] = {{{1,2,3},{4,5,6}}, {{7,8,9},{10,11,12}}};
    arr[1][0][2] = arr[0][1][1] + arr[1][1][0];
    std::cout << arr[1][0][2];
    return 0;
}

A 15

B 11

C 9

D Error

💡 Hint

Check the values at arr[0][1][1] and arr[1][1][0] and add them.

arr[0][1][1] is 5 and arr[1][1][0] is 10, so 5 + 10 = 15.

🔧 Debug

advanced

Identify the error in 2D array initialization

What error will this code produce?

C++

#include <iostream>
int main() {
    int arr[2][2] = {1, 2, 3, 4, 5};
    std::cout << arr[1][1];
    return 0;
}

A Runtime error: out of bounds access

B Outputs 5

C Outputs 4

D Compilation error: too many initializers

💡 Hint

Check how many values are allowed for a 2x2 array.

The array size is 2x2=4 but 5 values are given, causing a compilation error.

❓ Predict Output

advanced

Sum of elements in jagged 2D array simulation

What is the output of this code simulating a jagged array using pointers?

C++

#include <iostream>
int main() {
    int row1[] = {1, 2};
    int row2[] = {3, 4, 5};
    int* arr[2] = {row1, row2};
    int sizes[2] = {2, 3};
    int sum = 0;
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < sizes[i]; j++) {
            sum += arr[i][j];
        }
    }
    std::cout << sum;
    return 0;
}

A 12

B 14

C 15

D Error

💡 Hint

Add all elements in both rows carefully.

Sum is 1+2+3+4+5 = 15.

🧠 Conceptual

expert

Memory layout of multi-dimensional arrays

In C++, how are multi-dimensional arrays stored in memory?

A Row-major order: rows stored contiguously, then columns

B Each element stored at random memory locations

C Random order depending on compiler

D Column-major order: columns stored contiguously, then rows

💡 Hint

Think about how arrays are laid out in C++ standard.

C++ stores multi-dimensional arrays in row-major order, meaning all elements of a row are stored next to each other in memory.