Multidimensional Array | Programming and Data Structures - Computer Science Engineering (CSE) PDF Download

A multi-dimensional array is an array of arrays. 2-dimensional arrays are the most commonly used. They are used to store data in a tabular manner.
Consider the following 2D array, which is of size 3 x 5. For an array of size $N \times M$N×M, the rows and columns are numbered from $0$0 to $N - 1$N−1 and columns are numbered from $0$0 to $M - 1$M−1, respectively. Any element of the array can be accessed by arr[i][j] where $0 \leq i < N$0≤i<N and $0 \leq j < M$0≤j<M. For example, in the following array, the value stored at arr[1][3] is 14.

2D array declaration

To declare a 2D array, you must specify the following:

• Row-size: Defines the number of rows
• Column-size: Defines the number of columns
• Type of array: Defines the type of elements to be stored in the array, i.e., either a number, character, or other such datatype.

A sample form of declaration is as follows:
type arr[row_size][column_size];

A sample C array is declared as follows:

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int arr[3][5];

2D array initialization

An array can either be initialized during or after declaration.
The format of initializing an array during declaration is as follows:
type arr[row_size][column_size] = {{elements}, {elements} ... };

An example in C is given below:

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int arr[3][5] = {{5, 12, 17, 9, 3}, {13, 4, 8, 14, 1}, {9, 6, 3, 7, 21}};

Initializing an array after declaration can be done by assigning values to each cell of the 2D array, as follows:

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type arr[row_size][column_size];
arr[i][j] = 14;

A C example of initializing an array after declaration by assigning values to each cell of a 2D array is as follows:

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int arr[3][5];
arr[0][0] = 5;
arr[1][3] = 14;

This is quite naive and not usually used. Instead, the array elements are read from stdin.

Processing 2D arrays

The most basic form of processing is to loop over the array and print all its elements, which can be done as follows:

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type arr[row_size][column_size] = {{elements}, {elements} ... };
for(i = 0; i < row_size; i++)
    for(j = 0; j < column_size; j++)
        print arr[i][j];

A C example of looping over the array and printing all its elements is as follows:

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#include <stdio.h>
int main()
{
    // Array declaration and initialization
    int arr[3][5] = {{5, 12, 17, 9, 3}, {13, 4, 8, 14, 1}, {9, 6, 3, 7, 21}};
    // Iterate over the array
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 5; j++)
        {
            // Print out each element
            printf("%d ", arr[i][j]);
        }
        // Print new line character after the row is printed in the above loop
        printf("\n");
    }
    return 0;
}

These methods of declaration, initialization, and processing can be extended to 3D or higher-dimensional arrays.