Returning the lowest and highest number based on input
If you are only worried about showing Min and Max, and nothing else is the desired result then why not use an immediate calculation approach like this? It surely does not store unnecessary inputs - 

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int max = Int32.MinValue, min = Int32.MaxValue;
            int value = 0;

            while (int.TryParse(Console.ReadLine(), out value))
            {
                max = Math.Max(max, value);
                min = Math.Min(min, value);

                Console.WriteLine(" lowest is {0} ", min);
                Console.WriteLine(" highest is {0} ", max);
            }
        }
    }
}


This program will print min and max, until a non-digit character is given.