using System;

using System.Collections.Generic;

public class Program

{

    // Enumerate all possible m-size combinations of [0, 1, ..., n-1] array

    // in lexicographic order (first [0, 1, 2, ..., m-1]).

    private static IEnumerable<int[]> CombinationsRosettaWoRecursion(int m, int n)

    {

        int[] result = new int[m];

        Stack<int> stack = new Stack<int>(m);

        stack.Push(0);

        while (stack.Count > 0)

        {

            int index = stack.Count - 1;

            int value = stack.Pop();

            while (value < n)

            {

                result[index++] = value++;

                stack.Push(value);

                if (index != m) continue;

                yield return (int[])result.Clone(); // thanks to @xanatos

                //yield return result;

                break;

            }

        }

    }

​

    public static IEnumerable<T[]> CombinationsRosettaWoRecursion<T>(T[] array, int m)

    {

        if (array.Length < m)

            throw new ArgumentException("Array length can't be less than number of selected elements");

        if (m < 1)

            throw new ArgumentException("Number of selected elements can't be less than 1");

        T[] result = new T[m];

        foreach (int[] j in CombinationsRosettaWoRecursion(m, array.Length))

        {

            for (int i = 0; i < m; i++)

            {

                result[i] = array[j[i]];

            }

            yield return result;

        }

    }

// Driver code  

static public void Main () 

{ 

    int[] intArray = new int[]{ 2,4,8, 9};

    var arrayLen = intArray.Length;

    for(var i = arrayLen;i > 0; i--){

        var result = CombinationsRosettaWoRecursion(intArray,i);

        foreach(var line in result){

​

            var dvalue = string.Join(",", line);

            Console.WriteLine(dvalue);

        }

    }

}  

​

}

​

​