using System;

 using System.Linq;

 namespace Linq101

 {

     class QueryExecution

     {

         /// <summary>

         /// The following sample shows how query execution is deferred until the query is enumerated at a foreach statement.

         /// </summary>

         public void Linq99()

         {

             int[] numbers = new int[] { , , , , , , , , ,  };

             int i = ;

             //延迟执行

             var q = from n in numbers select ++i;

             foreach (int n in q)

             {

                 Console.WriteLine("n={0},i={1}", n, i);

             }

         }

         /// <summary>

         /// The following sample shows how queries can be executed immediately with operators such as ToList().

         /// </summary>

         public void Linq100()

         {

             int[] numbers = new int[] { , , , , , , , , ,  };

             int i = ;

             //ToList->立即执行

             var q = (from n in numbers select ++i).ToList();

             foreach (int n in q)

             {

                 Console.WriteLine("n={0},i={1}", n, i);

             }

         }

         /// <summary>

         /// The following sample shows how, because of deferred execution, queries can be used again after data changes and will then operate on the new data.

         /// </summary>

         public void Linq101()

         {

             int[] numbers = { , , , , , , , , ,  };

             //可重用

             var lowNumbers = from n in numbers

                              where n <=

                              select n;

             Console.WriteLine("First run numbers <=3:");

             foreach (int number in lowNumbers)

             {

                 Console.WriteLine(number);

             }

             lowNumbers = (from n in numbers select -n).ToArray();

             Console.WriteLine("Second run numbers <=3:");

             foreach (int number in lowNumbers)

             {

                 Console.WriteLine(number);

             }

         }

     }

 }