Jagged arrays are arrays in which member arrays can be of different sizes. It's like an array of arrays - each array element contains another array.

Jagged arrays are similar to multidimensional arrays, but have a minor difference. The multidimensional arrays have a fixed number of rows and columns where the jagged arrays can have a different number of columns in every row.

How to declare a jagged array?

For this example, declaring a jagged array with 5 columns:

int[][] x = new int[5][];

The second [] is initialized without a number. To initialize the sub-arrays, we need to do that separately as shown below,

for (int i = 0; i < x.length; i++) 
{
    x[i] = new int[10];
}

How to Get/Set values in a jagged array?

Now, getting one of the subarrays is easy. Let's print all the numbers of the 4th column of a:

for (int i = 0; i < x[3].length; i++)
{
    Console.WriteLine(x[3][i]);
}

Get a specific value:

x[<row_number>][<column_number>]

Set a specific value:

x[<row_number>][<column_number>] = <value>

Note: Jagged arrays (arrays of arrays) are faster and safe to use so use jagged arrays rather than multidimensional arrays (matrixes).

Order of the brackets to Note:

Consider a four-dimensional array of six-dimensional arrays of one-dimensional arrays of int. This should be written in C# as:

int[,,,][,,,,,][] arr = new int[3, 2, 10,6][,,,,,][];

In the CLR type system, the convention for the ordering of the brackets is reversed, so with the above arr the instance we have:

arr.GetType().ToString() == "System.Int32[][,,,,,][,,,]"

and likewise:

typeof(int[,,,][,,,,,][]).ToString() == "System.Int32[][,,,,,][,,,]"