Two-Dimensional Arrays

A 2D array is essentially an "array of arrays." It represents data in rows and columns, like a spreadsheet, a digital image, or a chess board.

Declaration

// data_type name[rows][columns];
int matrix[3][4]; // A grid with 3 rows and 4 columns (12 total items)

Initialization

int grid[2][3] = {
    {1, 2, 3}, // Row 0
    {4, 5, 6}  // Row 1
};

Accessing Elements

You need two indices: one for the row and one for the column.

int val = grid[1][0]; // Accesses the 4 (Row 1, Column 0)

Visual Table Representation

Processing with Nested Loops

To work with every item in a 2D array, you almost always use two nested for loops.

for (int i = 0; i < rows; i++) {       // Outer loop for rows
    for (int j = 0; j < columns; j++) { // Inner loop for columns
        printf("%d ", matrix[i][j]);
    }
    printf("\n"); // Newline after each row
}

Memory Layout: Row-Major Order

In your computer's RAM, memory is a single long line. Even a 2D array is stored linearly: all of Row 0 first, followed by all of Row 1, and so on.

Multi-Dimensional Arrays

You aren't limited to 2D. You can have 3D (a cube), 4D, or more.

int cube[10][10][10]; // 1000 integers total

While possible, anything above 3D is extremely difficult for humans to visualize and is rarely used in standard business logic.

When passing a 2D array to a function, you must specify the number of columns in the function parameter: void process(int arr[][3]). The compiler needs this to calculate the memory offsets!