Language Integrated Query (LINQ), which was introduced in C# 3.0, is a language feature of .NET Framework that enables us to query data in collections easily implementing the IEnumerable<T> interface, such as ArrayList<T>, List<T>, an XML document, and a database. It becomes easier to query any data in a collection since, using LINQ, we do not need to learn a different syntax for a different source of data. For instance, we don't need to learn SQL if we use LINQ when the data source is a database. Also, using LINQ, we don't have to learn XQuery when we deal with an XML document. Fortunately, LINQ has eased our use of a common syntax for all the sources of data.

There are two basic data units in LINQ; they are sequences, which include any object that implements IEnumerable<T>, and elements, which include the items in the sequence. Suppose we have the following int array named intArray:

int[] intArray = 
{ 
  0,  1,  2,  3,  4, ...