An array can contain more than simple datatypes: it can contains object. It can be objects from a custom class, or even … arrays, which are themselves objects!

Array of Objects From a Custom Class

In the following example, we will ask the user how many Item objects (the details of the implementation does not matter, but can be inspired by this example) they want to create, then fill an array with Item objects initialized from user input:

Console.WriteLine("How many items would you like to stock?");
Item[] items = new Item[int.Parse(Console.ReadLine())];
int i = 0;
while(i < items.Length)
{
    Console.WriteLine($"Enter description of item {i+1}:");
    string description = Console.ReadLine();
    Console.WriteLine($"Enter price of item {i+1}:");
    decimal price = decimal.Parse(Console.ReadLine());
    items[i] = new Item(description, price);
    i++;
}

Observe that, since we do not perform any user-input validation, we can simply use the result of int.Parse() as the size declarator for the items array - no size variable is needed at all.

We can also use while loops to search through arrays for a particular value. For example, this code will find and display the lowest-priced item in the array items, which was initialized by user input:

Item lowestItem = items[0];
int i = 1;
while(i < items.Length)
{
    if(items[i].GetPrice() < lowestItem.GetPrice())
    {
        lowestItem = items[i];
    }
    i++;
}
Console.WriteLine($"The lowest-priced item is {lowestItem}");

Note that the lowestItem variable needs to be initialized to refer to an Item object before we can call the GetPrice() method on it; we cannot call GetPrice() if lowestItem is null. We could try to create an Item object with the “highest possible” price, but a simpler approach is to initialize lowestItem with items[0]. As long as the array has at least one element, 0 is a valid index, and the first item in the array can be our first “guess” at the lowest-priced item.

Arrays of Arrays

An array of arrays is called a multi-dimensional array. A multi-dimensional array can be rectangular (it then represents an $n$-dimensional block of memory) or jagged (in that case, it is an array of arrays).

Rectangular Multi-Dimensional Array

Also called $2$-dimensional arrays, their syntax is very close to $1$-dimensional arrays:

int[,] matrix = new int[2, 3];

where 2 is the number of rows, and 3 is the number of columns. They can be accessed with matrix.GetLength(0) and matrix.GetLength(1) respectively.

Assignment is as for $1$-dimensional arrays, starting at $0$:

matrix[0, 0] = 1;
matrix[0, 1] = 2;
matrix[0, 2] = 3;
matrix[1, 0] = 4;
matrix[1, 1] = 5;
matrix[1, 2] = 6;

This will produce a matrix as follows:

We could also have used a shortened notation to declare this $2$-dimensional array, as follows:

int[,] matrix = new int[,]
{
    {1,2,3},
    {4,5,6}
};

or even simply

int[,] matrix = {{1,2,3},{4,5,6}};

To display such an array, nested loops are needed:

for (int row = 0; row < matrix.GetLength(0); row++)
{
    for (int col = 0; col < matrix.GetLength(1); col++)
        Console.Write(matrix[row, col] + " ");
    Console.WriteLine();
}

Jagged Array

A jagged array is an array of arrays. The difference with rectangular arrays is that the arrays stored can be of varying size.

The syntax is straightforward once understood that jagged arrays are exactly arrays of arrays:

int[][] jaggedArray = new int[3][];
jaggedArray[0] = new int[3] { 1, 2, 3};
jaggedArray[1] = new int [2]{ 4, 5};
jaggedArray[2] = new int[5] { 6, 7, 8, 9, 10};
 
for (int row = 0; row < jaggedArray.Length; row++)
{
    Console.Write("The row #" + row + " contain: ");
    for (int arrayCell = 0; arrayCell < jaggedArray[row].Length; arrayCell++)
    {
        Console.Write(jaggedArray[row][arrayCell]+ " " ); 
    }
    Console.WriteLine("");
} 

In this example, it should be clear that jaggedArray[row] is itself an array, and hence that we can use e.g., jaggedArray[row].Length or jaggedArray[row][arrayCell].