Let clause of LInq

   1:  class Program

   2:      {

   3:          /// <summary>

4: // let clause of LInq

5: // let: stores the results of a subexpression, which can be used in subsequent clauses.

6: // use the let keyword to complete this task. This keyword can create a new range variable and initialize the variable with the result of the expression you provide.

7: // once the range variable is initialized with a value, it cannot be used to store other values

8: // If the variable in this range is of the queryable type, you can query it.

   9:          /// </summary>

  10:          /// <param name="args"></param>

  11:          static void Main(string[] args)

  12:          {

13:/* instance:

14: * in the following example, let is used in two ways:

15: 1. Create an enumerative type that can be queried.

16: 2. Make the query only call ToLower once for the range variable word. If you do not use let, you must call ToLower in each predicate of the where clause.

  17:              */

  18:              string[] text = 

  19:              {

  20:                "A penny saved is a penny earned.",

  21:                "The early bird catches the worm.",

  22:                "The pen is mightier than the sword." 

  23:              };

24: var result = from sentence in text // The sentence range variable. The text array contains

25: let words = sentence. Split ('') // one piece of sentence is separated into one word by Split ('') and the result is stored in the words variable through "let ".

26: from word in words // The range variable word, which extracts a word from words.

27: let v = word. ToLower () // a word is converted by ToLower () and stored in another range variable v through "let ".

28: where v [0] = 'A' | v [0] = 'E' | v [0] = 'I' | v [0] = 'o' | v [0] = 'U' // filter each v variable (array) through the where key) the first element in is the "vowel" element.

29: select word; // word: entire word

  30:              foreach (var i in result)

  31:              {

32: Console. WriteLine ("\" {0} \ "starting with a vowel", I );

  33:              }

  34:              Console.ReadKey();

  35:   

  36:          }

  37:      }