IEnumerable接口和IEnumerator接口是.NET中非常重要的接口，二者有何区别？

    1. 简单来说IEnumerable是一个声明式的接口，声明实现该接口的类就是“可迭代的enumerable”,但并没用说明如何实现迭代器(iterator).其代码实现为：

         public interface IEnumerable
         {
                IEnumerator GetEnumerator();
          }
    2. 而IEnumerator接口是实现式接口，它声明实现该接口的类就可以作为一个迭代器iterator.其代码实现为：

        public interface IEnumerator
       {
                object Current { get; }

                bool MoveNext();
                void Reset();
        }

   3.一个collection要支持Foreach进行遍历，就必须实现IEnumerable,并一某种方式返回迭代器对象:IEnumerator.

   那么又如何实现这两个接口呢？ 其代码如下：

  假设有一个Person类，其有两个属性FirstName和LastName

  public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public Person(string firstName, string lastName)
        {
            this.FirstName = firstName;
            this.LastName = lastName;
        }
    }

另外通过People类来实现IEnumerable和IEnumerator接口.

//实现IEnumerable接口

public class People :IEnumerable

{

   public Person [] pers;

   public People(Person [] ps)

    {

      this.pers = ps;

    }

    public IEnumerator GetEnumerator()

    {

         //foreach(Person p in pers)

         // {

             //  yield return p;

          // }

      return new People1(pers);

      }

}

  //实现IEnumerator接口

   public class People1 : IEnumerator
    {
        public Person[] pers;
        public People1(Person[] per)
        {
            this.pers = per;
        }
        int position = -1;

        public bool MoveNext()
        {
            position++;
            return position < pers.Length;
        }
        public void Reset()
        {
            position=-1;
        }
        public object Current
        {
            get
            {
               try
               {
                   return pers[position];
               }
                catch(IndexOutOfRangeException ex)
                {
                    throw new InvalidOperationException();
                }
            }
        }
    }