C # foreach implementation,

C # foreach implementation,

Code 1:

        static void Main(string[] args)        {            int[] hs = { 1,2,3,4,5,6,7,8,9};            foreach (int item in hs)            {                Console.WriteLine(item.ToString());            }            Console.ReadKey();        }

Code 2:

        static void Main(string[] args)        {            ArrayList ArrLst = new ArrayList();            ArrLst.AddRange(new string[] { "jack","rose","joy","kristina"});            foreach (string s in ArrLst)            {                Console.WriteLine(s);            }            Console.ReadKey();        }

Code 3:

Using System; using System. collections; using System. collections. generic; using System. linq; using System. text; namespace ForeachDemo {class Dog {// constructor public Dog (params string [] dogNames) {DogNames. addRange (dogNames) ;}// name field and attribute private string Name; public string name {get {return name ;}set {name = value ;}} // List <string> Number of elements in the set public int DogNamesCounts () {return DogNames. count;} public List <string> DogNames = new List <string> (); // The public string this [int index] {get {return DogNames [index];} set {if (index> = DogNames. count) {DogNames. add (value) ;}else {DogNames [index] = value ;}}} class Program {static void Main (string [] args) {Dog D = new Dog ("husky", "GIWA", "Tibetan mastiff", "Shepherd Dog "); // for loop can access the object through the cited device // for (int I = 0; I <D. dogNames. count; I ++) // {// Console. writeLine (D [I]. toString (); // foreach cannot traverse foreach (string s in D) {Console. writeLine (s);} Console. readKey ();}}}

Q: Why can code 1 and Code 2 traverse int array elements through foreach loop?

Why code 3 cannot be accessed through foreach loop Traversal

Cause:

1. The Dog class does not implement the IEnumerable interface (in fact, you only need to have an enumerator method: public IEnumerator GetEnumerator ())

2. You must have a class to implement the IEnumerator interface.

See the following code:

Using System; using System. collections; using System. collections. generic; using System. linq; using System. text; namespace ForeachDemo {class Dog: IEnumerable {// constructor public Dog (params string [] dogNames) {DogNames. addRange (dogNames) ;}// name field and attribute private string Name; public string name {get {return name ;}set {name = value ;}} // List <string> Number of elements in the set public int DogNamesCounts () {return DogNames. count;} public List <string> DogNames = new List <string> (); // The public string this [int index] {get {return DogNames [index];} set {if (index> = DogNames. count) {DogNames. add (value) ;}else {DogNames [index] = value ;}}// here an IEnumerator-type object return value (IEnumerable explicitly) // IEnumerator IEnumerable. getEnumerator () // {// throw new NotImplementedException (); //} public IEnumerator GetEnumerator () {return new DogEnumerator (this. dogNames) ;}} public class DogEnumerator: IEnumerator {/* explicitly implements the IEnumerator interface object IEnumerator. current {get {throw new NotImplementedException () ;}} bool IEnumerator. moveNext () {throw new NotImplementedException ();} void IEnumerator. reset () {throw new NotImplementedException ();} * // constructor public DogEnumerator (List <string> paramDogNames) {this. dogsNames = paramDogNames;} List <string> dogsNames = new List <string> (); // The initial index of the enumerator, private int index =-1; // obtain the Current public object Current {get {if (index <0) {return null;} else {return dogsNames [index] ;}} in the Set // determine whether the number of enumerations can be pushed to the next element of the set public bool MoveNext () {index + = 1; if (index> = dogsNames. count) {return false;} else {return true ;}// set the number of enumerations to its initial position before the first element in the Set (the index is-1) public void Reset () {this. index =-1 ;}} class Program {static void Main (string [] args) {Dog D = new Dog ("husky", "GIWA", "Tibetan mastiff ", "sheepdog"); // for loop can access the object through the cited device // for (int I = 0; I <D. dogNames. count; I ++) // {// Console. writeLine (D [I]. toString (); //} foreach (string s in D) {Console. writeLine (s);} Console. readKey ();}}}