How to declare a two-dimensional array in C#

A two-dimensional array in C# is a data structure that stores elements in a grid-like format with rows and columns. It can be thought of as an array of arrays, where each element is accessed using two indices.

Syntax

Following is the syntax for declaring a two-dimensional array −

datatype[,] arrayName;

Following is the syntax for initializing a two-dimensional array −

datatype[,] arrayName = new datatype[rows, columns];

You can also declare and initialize in one statement −

datatype[,] arrayName = new datatype[rows, columns] {
    {value1, value2, ...},
    {value3, value4, ...},
    ...
};

Declaration and Initialization

Basic Declaration

You can declare a two-dimensional array without initialization −

using System;

class Program {
    static void Main() {
        int[,] numbers = new int[2, 3];
        
        // Assigning values
        numbers[0, 0] = 10;
        numbers[0, 1] = 20;
        numbers[0, 2] = 30;
        numbers[1, 0] = 40;
        numbers[1, 1] = 50;
        numbers[1, 2] = 60;
        
        Console.WriteLine("Element at [0,1]: " + numbers[0, 1]);
        Console.WriteLine("Element at [1,2]: " + numbers[1, 2]);
    }
}

The output of the above code is −

Element at [0,1]: 20
Element at [1,2]: 60

Declaration with Initialization

You can initialize a two-dimensional array at the time of declaration −

using System;

class Program {
    static void Main() {
        int[,] matrix = new int[3, 3] {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };
        
        // Display the matrix
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                Console.Write(matrix[i, j] + " ");
            }
            Console.WriteLine();
        }
    }
}

The output of the above code is −

1 2 3 
4 5 6 
7 8 9 

Using GetLength() Method

The GetLength() method returns the number of elements in a specified dimension. This is useful when you don't know the array size beforehand −

using System;

class Program {
    static void Main() {
        int[,] data = new int[3, 4] {
            {10, 20, 30, 40},
            {50, 60, 70, 80},
            {90, 100, 110, 120}
        };
        
        int rows = data.GetLength(0);    // Number of rows
        int cols = data.GetLength(1);    // Number of columns
        
        Console.WriteLine("Array dimensions: " + rows + " x " + cols);
        
        // Print all elements
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                Console.Write("data[" + i + "," + j + "] = " + data[i, j] + " ");
            }
            Console.WriteLine();
        }
    }
}

The output of the above code is −

Array dimensions: 3 x 4
data[0,0] = 10 data[0,1] = 20 data[0,2] = 30 data[0,3] = 40 
data[1,0] = 50 data[1,1] = 60 data[1,2] = 70 data[1,3] = 80 
data[2,0] = 90 data[2,1] = 100 data[2,2] = 110 data[2,3] = 120 

Conclusion

Two-dimensional arrays in C# provide an efficient way to store and manipulate data in a tabular format. They are declared using the [,] syntax and accessed using two indices representing row and column positions. Use the GetLength() method to determine array dimensions dynamically.