Enumerators and Foreach : Enum : Data Types C# Source Code

    

/*
A Programmer's Introduction to C# (Second Edition)
by Eric Gunnerson

Publisher: Apress  L.P.
ISBN: 1-893115-62-3
*/
// 19 - Indexers and Enumerators\Enumerators and Foreach
// copyright 2000 Eric Gunnerson
using System;
using System.Collections;

// Note: This class is not thread-safe
class IntList: IEnumerable
{
    int[] values = new int[10];
    int allocated = 10;
    int count = 0;
    int revision = 0;
    
    public void Add(int value)
    {
        // reallocate if necessary
        if (count + 1 == allocated)
        {
            int[] newValues = new int[allocated * 2];
            for (int index = 0; index < count; index++)
            {
                newValues[index] = values[index];
            }
            allocated *= 2;
        }        
        values[count] = value;
        count++;
        revision++;
    }
    
    public int Count
    {
        get
        {
            return(count);
        }
    }
    
    void CheckIndex(int index)
    {
        if (index >= count)
        throw new ArgumentOutOfRangeException("Index value out of range");
    }
    
    public int this[int index]
    {
        get
        {
            CheckIndex(index);
            return(values[index]);
        }
        set
        {
            CheckIndex(index);
            values[index] = value;
            revision++;
        }
    }
    
    public IEnumerator GetEnumerator()
    {
        return(new IntListEnumerator(this));
    }
    
    internal int Revision
    {
        get
        {
            return(revision);
        }
    }
}

class IntListEnumerator: IEnumerator
{
    IntList    intList;
    int revision;
    int index;
    
    internal IntListEnumerator(IntList intList)
    {
        this.intList = intList;
        Reset();
    }
    
    public bool MoveNext()
    {
        index++;
        if (index >= intList.Count)
        return(false);
        else
        return(true);
    }
    
    public object Current
    {
        get
        {
            if (revision != intList.Revision)
            throw new InvalidOperationException("Collection modified while enumerating.");
            return(intList[index]);
        }
    }
    
    public void Reset()
    {
        index = -1;
        revision = intList.Revision;
    }
}

public class EnumeratorsandForeach {
    public static void Main()
    {
        IntList list = new IntList();
        
        list.Add(1);
        list.Add(55);
        list.Add(43);
        
        foreach (int value in list)
        {
            Console.WriteLine("Value = {0}", value);
        }
        
        foreach (int value in list)
        {
            Console.WriteLine("Value = {0}", value);
            list.Add(124);
        }
    }
}