Descending, ascending

A descending sort goes from high to low. For C# strings it goes from the last alphabetical string to the first.

In a query expression, we use descending and ascending to indicate sort order. Ascending goes from low to high. These C# keywords encourage elegant and clear code.

An example

This program specifies a query expression (starting with from). The parts of query expressions that contain these keywords are query clauses.

using System;
using System.Linq;

// Part 1: create an integer array.
int[] array = { 1, 3, 5, 7, 9 };

// Part 2: select the elements in a descending order with query clauses.
var result = from element in array
             orderby element descending
             select element;

// Part 3: evaluate the query and display the results.
foreach (var element in result)
{
    Console.WriteLine($"DESCENDING: {element}");
}
DESCENDING: 9
DESCENDING: 7
DESCENDING: 5
DESCENDING: 3
DESCENDING: 1

Ascending

There is an ascending keyword that can be used in the same context as the descending keyword (following an orderby clause). Ascending sorts are normally the default.

using System;
using System.Linq;

class Employee
{
    public int Salary { get; set; }
    public int Id { get; set; }
}

class Program
{
    static void Main()
    {
        Employee[] array = new Employee[]
        {
            new Employee(){Salary = 40000, Id = 4},
            new Employee(){Salary = 40000, Id = 0},
            new Employee(){Salary = 60000, Id = 7},
            new Employee(){Salary = 60000, Id = 9}
        };

        // Highest salaries first.
        // ... Lowest IDs first.
        var result = from em in array
                     orderby em.Salary descending, em.Id ascending
                     select em;

        foreach (var em in result)
            Console.WriteLine("{0}, {1}", em.Salary, em.Id);
    }
}
60000, 7
60000, 9
40000, 0
40000, 4

Multiple properties

Query expressions provide an intuitive syntax for sorting on 2 properties at once. The first property specified in the orderby clause is the primary sort.

Ascending, notes

Because ascending is the default, you don't need to specify it. You can just omit this keyword and the query expression will function the same way.

Contextual

The descending keyword is only considered a keyword in certain cases. The C# compiler provides a special-cased parser for query expressions.

A summary

Descending and ascending indicate the progression of an orderby clause in a query expression. The query clause is translated to method syntax before being executed.