Two-Dimensional Arrays in C

C supports multi-dimensional arrays through a straightforward declaration syntax:

type arrayName[size1][size2];

A three-dimensional integer array with dimensions 5×10×4 would be declared as:

int cuboid[5][10][4];

The most common multi-dimensional array is the two-dimensional array, which can be visualized as a table with rows and columns. To declare an array with x rows and y columns:

type arrayName[x][y];

For example, a table with 3 rows and 4 columns:

int matrix[3][4];

Each element is accessed using the notation matrix[i][j], where i represents the row index and j represents the column index.

Initializing Two-Dimensional Arrays

Arrays can be initialized by specifying values for each row within curly braces:

int data[3][4] = {
    {0, 1, 2, 3},
    {4, 5, 6, 7},
    {8, 9, 10, 11}
};

The nested braces are optional. The equivalent single-line initialization:

int data[3][4] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};

Accessing Array Elements

Element are accessed using row and column indices. The following retrieves the element at row 2, column 3:

int value = data[2][3];

Practical Example

The following program demonstrates array enitialization and element access using nested loops:

#include <stdio.h>

int main(void)
{
    int values[5][2] = {
        {0, 0},
        {1, 2},
        {2, 4},
        {3, 6},
        {4, 8}
    };
    int row, col;

    for (row = 0; row < 5; row++)
    {
        for (col = 0; col < 2; col++)
        {
            printf("values[%d][%d] = %d\n", row, col, values[row][col]);
        }
    }

    return 0;
}

Output:

values[0][0] = 0
values[0][1] = 0
values[1][0] = 1
values[1][1] = 2
values[2][0] = 2
values[2][1] = 4
values[3][0] = 3
values[3][1] = 6
values[4][0] = 4
values[4][1] = 8

While C supports arrays of any dimension, one-dimensional and two-dimensional arrays are the most frequently used in practice.

Passing Arrays to Functions

When passing an array to a function, the parameter can be declared in three equivalent ways. Each approach informs the compiler that it will receive a pointer to an integer.

Parameter as a Pointer

void processArray(int *arr)
{
    /* function body */
}

Parameter as a Sized Array

void processArray(int arr[10])
{
    /* function body */
}

Parameter as an Unsized Array

void processArray(int arr[])
{
    /* function body */
}

Complete Example

The following function calculates the average of array elements:

#include <stdio.h>

double calculateAverage(int numbers[], int length);

int main(void)
{
    int scores[] = {1000, 2, 3, 17, 50};
    double result;

    result = calculateAverage(scores, 5);
    printf("Average: %.2f\n", result);

    return 0;
}

double calculateAverage(int numbers[], int length)
{
    int index;
    double avg;
    double total = 0.0;

    for (index = 0; index < length; index++)
    {
        total += numbers[index];
    }

    avg = total / length;
    return avg;
}

Output:

Average: 214.40

Note that the array dimension is irrelevant within the function, as C does not perform bounds checking on array parameters.