Algorithem QuickSort.

/// <summary>
        /// Implement the Quick Sort algorithm.
        /// </summary>
        /// <param name="ArrayEx">The array will be sorted</param>
        /// <param name="start">the index of the first element of the array</param>
        /// <param name="end">the last index of the array</param>
        public static void QuickSort(int[] ArrayEx, int start, int end)
        {

            if (end - start > 0) // the length of the array must be greater than 1.
            {
                int pivot = ArrayEx[end];//set the last menber to the pivot
                //You can choose one in the array anywhere
                int j = start;           //set a pointer
                for (int i = start; i <= end; i++)
                {
                    if (ArrayEx[i] < pivot)
                    {
                        swap(ref ArrayEx[i], ref ArrayEx[j]);
                        j++;//swap the value and than the j point the next one.
                    }
                }
                swap(ref ArrayEx[j], ref ArrayEx[end]);
                // *************************************************************************************************
                // depart the array into two piececs than call the method again till the length of the piecec is one.
                // *************************************************************************************************
                QuickSort(ArrayEx, start, j - 1);
                QuickSort(ArrayEx, j + 1, end);
            }
        }