Resizable array

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Resizable_array
{
    class Program
    {
        static void Main(string[] args)
        {
            int?[] array = new int?[4];
            int index = 0;
            int overflow = 3;
            string[] command = Console.ReadLine().Split(' ').ToArray();
            while (command [0] != "end")
            {
                if (command[0] == "push")
                {
                    array[index] = int.Parse(command[1]);
                    index++;
                }
                else if (command [0] == "pop")
                {
                    array[index-1] = null;
                    index--;
                }
                else if (command[0] == "removeAt")
                {
                    int removeIndex = int.Parse(command[1]);
                    for (int i = removeIndex; i < index; i++)
                    {
                        array[i] = array[i + 1];
                        array[i + 1] = null;
                    }
                    index--;
                }
                else if (command[0] == "clear")
                {
                    for (int i = 0; i < index; i++)
                    {
                        array[i] = null;
                    }
                    index = 0;
                }
                if (index == overflow)
                {
                    int?[] tempArray = new int?[overflow + 1];
                    Array.Copy(array, tempArray, overflow + 1);
                    overflow += 4;
                    array = new int?[overflow + 1];
                    Array.Copy(tempArray, array, overflow - 3);
                }
                command = Console.ReadLine().Split(' ').ToArray();
            }
            if (index <= 0)
            {
                Console.Write("empty array");
            }
            else
            {
                for (int i = 0; i <= index; i++)
                {
                    Console.Write("{0} ", array[i]);
                }
            }
            Console.WriteLine();
        }
    }
}