Multi-dimensional arrays in C++ - Mini Project: Build & Apply

Working with Multi-dimensional Arrays in C++

📖 Scenario: You are organizing seating for a small movie theater. The theater has 3 rows and 4 seats in each row. You want to keep track of how many people are sitting in each seat.

🎯 Goal: Create a 2D array to represent the seats, fill it with some numbers, then calculate the total number of people seated in the theater.

📋 What You'll Learn

Create a 2D array called seats with 3 rows and 4 columns

Initialize the array with exact values for each seat

Create an integer variable called totalPeople to hold the sum

Use nested for loops with variables row and col to iterate over seats

Add the number of people in each seat to totalPeople

Print the total number of people using std::cout

💡 Why This Matters

🌍 Real World

Multi-dimensional arrays are used to represent grids, tables, or matrices such as seating charts, game boards, or pixel data in images.

💼 Career

Understanding multi-dimensional arrays is essential for software developers working with data structures, graphics, simulations, and many other fields.

1

Create the 2D array seats

Create a 2D array called seats with 3 rows and 4 columns. Initialize it with these exact values: first row {1, 0, 2, 1}, second row {0, 3, 1, 0}, third row {2, 1, 0, 1}.

C++

#include 

int main() {
    // Create the 2D array seats with given values
    // Your code here

    return 0;
}

Hint

Use int seats[3][4] = { ... }; to create and initialize the array.

2

Create the variable totalPeople

Create an integer variable called totalPeople and set it to 0. This will hold the total number of people seated.

C++

#include 

int main() {
    int seats[3][4] = {
        {1, 0, 2, 1},
        {0, 3, 1, 0},
        {2, 1, 0, 1}
    };

    // Create totalPeople variable and set to 0
    // Your code here

    return 0;
}

Hint

Use int totalPeople = 0; to create and initialize the variable.

3

Sum all people using nested for loops

Use nested for loops with variables row and col to iterate over the seats array. Add each seat's value to totalPeople.

C++

#include 

int main() {
    int seats[3][4] = {
        {1, 0, 2, 1},
        {0, 3, 1, 0},
        {2, 1, 0, 1}
    };

    int totalPeople = 0;

    // Use nested for loops to add all seat values to totalPeople
    // Your code here

    return 0;
}

Hint

Use two for loops: outer loop for rows, inner loop for columns. Add each seat value to totalPeople.

4

Print the total number of people

Use std::cout to print the text Total people seated: followed by the value of totalPeople.

C++

#include 

int main() {
    int seats[3][4] = {
        {1, 0, 2, 1},
        {0, 3, 1, 0},
        {2, 1, 0, 1}
    };

    int totalPeople = 0;

    for (int row = 0; row < 3; row++) {
        for (int col = 0; col < 4; col++) {
            totalPeople += seats[row][col];
        }
    }

    // Print the total number of people
    // Your code here

    return 0;
}

Hint

Use std::cout << "Total people seated: " << totalPeople << std::endl; to print the result.

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