[C#] TextRPG

  using System;

  namespace TextRPG
  {
    class Program
    {
      
      enum ClassType
      {
        None = 0,
        Knight = 1,
        Archer = 2,
        Magicion = 3
      }

      struct Player
      {
        public int hp;
        public int attack;
      }

      enum MonsterType
      {
        None = 0,
        Slime = 1,
        Orc = 2,
        Skeleton = 3
      }

      struct Monster
      {
        public int hp;
        public int attack;
      }

      static ClassType ChooseClass()
      {
        Console.WriteLine("Select your position!");
        Console.WriteLine("[1] Knight");
        Console.WriteLine("[2] Archer");
        Console.WriteLine("[3] Magicion");

        ClassType choice = ClassType.None;
        string input = Console.ReadLine();

        switch (input)
        {
          case "1":
            choice = ClassType.Knight;
            break;
          case "2":
            choice = ClassType.Archer;
            break;
          case "3":
            choice = ClassType.Magicion;
            break;
        }

        return choice;
      }

      static void CreatePlayer(ClassType choice, out Player player)
      {
        // Knight(100/10) Archer(75/12) magicion(50/15)
        switch (choice)
        {
          case ClassType.Knight:
            player.hp = 100;
            player.attack = 10;
            break;
          case ClassType.Archer:
            player.hp = 75;
            player.attack = 12;
            break;
          case ClassType.Magicion:
            player.hp = 50;
            player.attack = 15;
            break;
          default:
            player.hp = 0;
            player.attack = 0;
            break;
        }
      }

      static void CreateRandomMonster(out Monster monster)
      {
        Random rand = new Random();
        int randMonster = rand.Next(1, 4);

        switch (randMonster)
        {
          case (int)MonsterType.Slime:
            monster.hp = 20;
            monster.attack = 2;
            Console.WriteLine("Slime is responed!");
            break;
          case (int)MonsterType.Orc:
            monster.hp = 40;
            monster.attack = 4;
            Console.WriteLine("Orc is responed!");
            break;
          case (int)MonsterType.Skeleton:
            monster.hp = 30;
            monster.attack = 3;
            Console.WriteLine("Skeleton is responed!");
            break;
          default:
            monster.hp = 0;
            monster.attack = 0;
            break;
        }
      }

      static void Fight(ref Player player, ref Monster monster)
      {
        while (true)
        {
          // Player attacks monster
          monster.hp -= player.attack;

          if (monster.hp <= 0)
          {
            Console.WriteLine("You Win! :)");
            Console.WriteLine($"Your hp : {player.hp}");
            break;
          }

          // Monster attacks player
          player.hp -= monster.attack;
  
          if (player.hp <= 0)
          {
            Console.WriteLine("You Lose! :(");
            break;
          }
        }
      }

      static void EnterField(ref Player player)
      {
        while (true)
        {
          Console.WriteLine("You entered field!");

          // Create Monster
          Monster monster;

          // Respon one monster among 3 random monsters
          CreateRandomMonster(out monster);

          Console.WriteLine("[1] Change Battle Mode");
          Console.WriteLine("[2] Run away to town with a certain chance");

          String input = Console.ReadLine();
          if (input == "1")
          {
            Fight(ref player, ref monster);
          }
          else if (input == "2")
          {
            // Run away chance: 33%
            Random rand = new Random();
            int randValue = rand.Next(0, 101);

            if (randValue <= 33)
            {
              Console.WriteLine("You successed to run away!");
              break;
            }
            else
            {
              Fight(ref player, ref monster);
            }
          }
        }
      }

      static void EnterGame(ref Player player)
      {
        while (true)
        {
          Console.WriteLine("You entered town!");
          Console.WriteLine("[1] Go to field.");
          Console.WriteLine("[2] Return to lobby.");

          string input = Console.ReadLine();
          if (input == "1")
          {
            EnterField(ref player);
          }
          else if (input == "2")
          {
            break;
          }
        }
      }

      static void Main(string[] args)
      {
        while (true)
        {
          ClassType choice = ChooseClass();
          if (choice == ClassType.None)
            continue;

          // Create Player
          Player player;
          CreatePlayer(choice, out player);
 
          // Go to field and fight with monster
          EnterGame(ref player);
        }
      }
    }
  }

  static void Fight(ref Player player, ref Monster monster)

  static void CreatePlayer(ClassType choice, out Player player)