C# Error

using System.IO;
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public struct Player
{
    public string Name;
    public string Nickname;
}

public class Application
{
    static void Main()
    {
        int i = 0;
        Console.WriteLine("Enter number of players:");
        int num_players = Convert.ToInt32(Console.ReadLine());
        Player[] players = new Player[num_players];
        for(i = 0; i < num_players; i++)
        {
            Console.WriteLine("Player Name:");
            players[i].Name = Console.ReadLine();
            Console.WriteLine("Player Nickname:");
            players[i].Nickname = Console.ReadLine();
        }
        foreach(Player x in players)
        {
            Console.WriteLine("Player Name: " + x.Name);
            Console.WriteLine("Player Nickname: " + x.Nickname);
        }
        Console.WriteLine("Quantos Players?");
        num_players = Convert.ToInt32(Console.ReadLine());
        Array.Resize(ref players, num_players);
        for(int k = 0; k == num_players; k--)
        {
            players[k] = players[k + 1];
        }
        for(; i < num_players; i++)
        {
            Console.WriteLine("Player Name:");
            players[i].Name = Console.ReadLine();
            Console.WriteLine("Player Nickname:");
            players[i].Nickname = Console.ReadLine();
        }
        foreach(Player x in players)
        {
            Console.WriteLine("Player Name: " + x.Name);
            Console.WriteLine("Player Nickname: " + x.Nickname);
        }
        string file_directory = @"Cache.txt";
        using (StreamWriter sw = File.CreateText(file_directory))
        {
            for(int k = 0; k < num_players; k++)
            {
                sw.WriteLine(players[k].Name);
                sw.WriteLine(players[k].Nickname);
            }
        }
        using (StreamReader sr = File.OpenText(file_directory))
        {
            string s = "";
            do{
                s = sr.ReadLine();
                if(s == null)
                {
                    num_players = num_players + 1;
                    Array.Resize(ref players, num_players);
                    players[num_players].Name = s;
                }
                s = sr.ReadLine();
                if(s == null)
                {
                    players[num_players].Nickname = s;
                }
            } while (s != null);
        }
        foreach(Player x in players)
        {
            Console.WriteLine(x.Name);
            Console.WriteLine(x.Nickname);
        }
        Console.ReadKey();
    }
}