Multidimensional Arrays

Multidimensional Arrays

Multidimensional arrays are arrays that contain more than one dimension. The most common type is the two-dimensional array, which can be thought of as a table with rows and columns. Each element in a multidimensional array can be accessed using multiple indices.

Declaring Multidimensional Arrays

To declare a two-dimensional array in C++, you specify the type of the elements, followed by the name of the array and the sizes of each dimension in square brackets. For example:

int myArray[3][4];

This declaration creates an array named myArray with 3 rows and 4 columns. The total number of elements in this array is 3 × 4 = 12.

Initialising Multidimensional Arrays

You can initialise a two-dimensional array at the time of declaration. For example:

int myArray[2][3] = { {1, 2, 3}, {4, 5, 6} };

This creates a 2 × 3 array with the first row containing 1, 2, 3 and the second row containing 4, 5, 6.

Accessing Elements in Multidimensional Arrays

To access an element in a multidimensional array, you use the array name followed by the indices in square brackets. For example, to access the element in the second row and third column:

int value = myArray[1][2];

This code assigns the value 6 to the variable value, as it corresponds to the element in the second row and third column of myArray.

Iterating Through Multidimensional Arrays

To iterate through a two-dimensional array, you can use nested loops. The outer loop iterates through the rows, and the inner loop iterates through the columns. Here is an example:

for (int i = 0; i < 2; i++) {  // Iterate through rows
    for (int j = 0; j < 3; j++) {  // Iterate through columns
        std::cout << myArray[i][j] << " ";
    }
    std::cout << std::endl;  // New line after each row
}

This code will print all the elements of myArray in a tabular format.

Multidimensional Arrays with More Than Two Dimensions

While two-dimensional arrays are common, C++ also supports arrays with more than two dimensions. The syntax is similar. For example, to declare a three-dimensional array:

int my3DArray[2][3][4];

This creates an array with 2 layers, 3 rows, and 4 columns. You can access an element in a three-dimensional array using three indices:

int value = my3DArray[1][2][3];

Example: Using a Multidimensional Array

Let’s create a simple program that uses a two-dimensional array to store and display the marks of students in different subjects:

#include 
using namespace std;

int main() {
    int marks[3][4] = { {75, 85, 90, 80},
                         {65, 70, 75, 80},
                         {85, 90, 95, 100} };

    cout << "Marks of Students:\n";
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 4; j++) {
            cout << marks[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}

This program declares a 3 × 4 array called marks and initialises it with the marks of three students in four subjects. It then uses nested loops to print the marks.

Dynamic Multidimensional Arrays

In C++, you can also create multidimensional arrays dynamically using pointers and the new operator. Here is an example of how to create a dynamic two-dimensional array:

int rows = 3;
int cols = 4;
int **dynamicArray = new int*[rows];
for (int i = 0; i < rows; i++) {
    dynamicArray[i] = new int[cols];
}

In this code, we first allocate memory for an array of pointers, and then for each pointer, we allocate an array of integers.

Freeing Dynamic Multidimensional Arrays

To free a dynamic two-dimensional array, you need to delete each row first, and then delete the array of pointers:

for (int i = 0; i < rows; i++) {
    delete[] dynamicArray[i];
}
delete[] dynamicArray;

Common Mistakes with Multidimensional Arrays

Summary

• Multidimensional arrays allow you to store data in more than one dimension.
• Two-dimensional arrays are the most common type, resembling tables.
• Access elements using multiple indices.
• Use nested loops to iterate through the elements.
• Dynamic multidimensional arrays can be created using pointers.

Check your understanding

• What is the syntax for declaring a two-dimensional array in C++?
• How do you access an element in a two-dimensional array?
• What is a common mistake when working with multidimensional arrays?
• Explain how to free memory allocated for a dynamic multidimensional array.