C# program to sort number strings

using System;
using System.Collections.Generic;
namespace SortStrings
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] inputArray = {"324", "1", "9001", "-23", "99", "324", "800", "801", "802", "888" };
            Console.WriteLine("Input array is :");
            DisplayArray(ref inputArray);
            QuickSort(ref inputArray, 0, inputArray.Length-1);
            Console.WriteLine("Sorted array is :");
            DisplayArray(ref inputArray);
            Console.ReadKey();
        }
        private static void DisplayArray(ref string[] inputArray)
        {
            foreach (string s in inputArray)
            {
                Console.WriteLine(s);
            }
        }
        private static int Partition(ref string[] inputArray, int startIndex, int endIndex)
        {
            int loopIndex = startIndex;
            int lastIndex = startIndex;
            CompareNumberString c = new CompareNumberString();
            IComparer<string> comparer = (IComparer<string>)c;
            while (loopIndex < endIndex)
            {
                if (comparer.Compare(inputArray[loopIndex], inputArray[endIndex]) < 0)
                {
                    swap(ref inputArray, loopIndex, lastIndex);
                    lastIndex++;
                }
                loopIndex++;
            }
            swap(ref inputArray, endIndex, lastIndex);
            return lastIndex;
        }
        private static void QuickSort(ref string[] inputArray, int startIndex, int endIndex)
        {
            if (startIndex >= endIndex)
            {
                return;
            }       
            int pivotIndex = Partition(ref inputArray, startIndex, endIndex);
            QuickSort(ref inputArray, startIndex, pivotIndex - 1);
            QuickSort(ref inputArray, pivotIndex + 1, endIndex);
            return;
        }
        private static void swap(ref string[] inputArray, int index1, int index2)
        {
            string temp = inputArray[index1];
            inputArray[index1] = inputArray[index2];
            inputArray[index2] = temp;
        }
    }
}