Program.cs

public class Program
{
    public char[] boardPositions = { '1', '2', '3', '4', '5', '6', '7', '8', '9' };

    public char playerCharacter = ' ';

    public bool gameEnded = false;

    public void DrawBoard()
    {
        Console.Clear();
        // Draw row 1 of the board
        Console.WriteLine("  -------------------------");
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  |   {0}   |   {1}   |   {2}   |", boardPositions[0], boardPositions[1], boardPositions[2]);
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  -------------------------");
        // Draw row 2 of the board
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  |   {0}   |   {1}   |   {2}   |", boardPositions[3], boardPositions[4], boardPositions[5]);
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  -------------------------");
        // Draw row 3 of the board
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  |   {0}   |   {1}   |   {2}   |", boardPositions[6], boardPositions[7], boardPositions[8]);
        Console.WriteLine("  |       |       |       |");
        Console.WriteLine("  -------------------------");
    }

    public void Play(int player, int input)
    {
        if (player == 1) playerCharacter = 'X';
        else if (player == 2) playerCharacter = 'O';

        switch (input)
        {
            case 1: boardPositions[0] = playerCharacter; break;
            case 2: boardPositions[1] = playerCharacter; break;
            case 3: boardPositions[2] = playerCharacter; break;
            case 4: boardPositions[3] = playerCharacter; break;
            case 5: boardPositions[4] = playerCharacter; break;
            case 6: boardPositions[5] = playerCharacter; break;
            case 7: boardPositions[6] = playerCharacter; break;
            case 8: boardPositions[7] = playerCharacter; break;
            case 9: boardPositions[8] = playerCharacter; break;
        }

    }

    public void HorizontalWin()
    {
        char[] playerCharacters = { 'X', 'O' };

        foreach (char playerCharacter in playerCharacters)
        {   
            if (((boardPositions[0] == playerCharacter) && (boardPositions[1] == playerCharacter) && (boardPositions[2] == playerCharacter))
                || ((boardPositions[3] == playerCharacter) && (boardPositions[4] == playerCharacter) && (boardPositions[5] == playerCharacter))
                || ((boardPositions[6] == playerCharacter) && (boardPositions[7] == playerCharacter) && (boardPositions[8] == playerCharacter)))
            {
            Console.Clear();
            if (playerCharacter == 'X')
            {
                Console.WriteLine("Congratulations Player 1.\nYou have achieved a horizontal win! ");
            }
            else if (playerCharacter == 'O')
            {
                Console.WriteLine("Congratulations Player 2.\nYou have achieved a horizontal win! ");
            }
            gameEnded = true;
            Console.WriteLine("Please press any key to reset the game");
            Console.ReadKey();
            ResetBoard();
            break;
            }
        }
    }

    public void VerticalWin()
    {
        char[] playerCharacters = { 'X', 'O' };

        foreach (char playerCharacter in playerCharacters)
        {
            if (((boardPositions[0] == playerCharacter) && (boardPositions[3] == playerCharacter) && (boardPositions[6] == playerCharacter))
                || ((boardPositions[1] == playerCharacter) && (boardPositions[4] == playerCharacter) && (boardPositions[7] == playerCharacter))
                || ((boardPositions[2] == playerCharacter) && (boardPositions[5] == playerCharacter) && (boardPositions[8] == playerCharacter)))
            {
                Console.Clear();
                if (playerCharacter == 'X')
                {
                    Console.WriteLine("Congratulations Player 1.\nYou have achieved a vertical win!");
                }
                else
                {
                    Console.WriteLine("Congratulations Player 2.\nYou have achieved a vertical win!");
                }
                gameEnded = true;
                Console.WriteLine("Please press any key to reset the game");
                Console.ReadKey();
                ResetBoard();
                break;
            }
        }
    }

    public void DiagonalWin()
    {
        char[] playerCharacters = { 'X', 'O' };

        foreach (char playerCharacter in playerCharacters)
        {
            if (((boardPositions[0] == playerCharacter) && (boardPositions[4] == playerCharacter) && (boardPositions[8] == playerCharacter))
                || ((boardPositions[6] == playerCharacter) && (boardPositions[4] == playerCharacter) && (boardPositions[2] == playerCharacter)))
            {
                Console.Clear();
                if (playerCharacter == 'X')
                {
                    Console.WriteLine("Congratulations Player 1.\nYou have achieved a diagonal win!");
                }
                else
                {
                    Console.WriteLine("Congratulations Player 2.\nYou have achieved a diagonal win!");
                }
                gameEnded = true;
                Console.WriteLine("Please press any key to reset the game");
                Console.ReadKey();
                ResetBoard();
                break;
            }
        }
    }

    public void Draw()
    {
        if (boardPositions[0] != '1' && boardPositions[1] != '2' && boardPositions[2] != '3' && boardPositions[3] != '4' && boardPositions[4] != '5'
            && boardPositions[5] != '6' && boardPositions[6] != '7' && boardPositions[7] != '8' && boardPositions[8] != '9')
        {
            Console.Clear();
            Console.WriteLine("It's a draw!");
            gameEnded = true;
            Console.WriteLine("Please press any key to reset the game");
            Console.ReadKey();
            ResetBoard();
        }
    }

    public void ResetBoard()
    {
        char[] ArrBoardInitialize = { '1', '2', '3', '4', '5', '6', '7', '8', '9' };
        boardPositions = ArrBoardInitialize;
        DrawBoard();
        gameEnded = false;
    }

    static void Main(string[] args)
    {
        //Set the console to white and text to black
        Console.BackgroundColor = ConsoleColor.White;
        Console.Clear();
        Console.ForegroundColor = ConsoleColor.Black;

        Program program = new Program();
        int currentTurn = 1;
        int playerInput = 0;
        bool validInputGiven = true;

        while (!program.gameEnded)
        {
            program.DrawBoard();
            validInputGiven = false;
            while (!validInputGiven)
            {
                Console.WriteLine("\nReady Player {0}: It's your move!", currentTurn);
                try
                {
                    if (currentTurn == 2)
                    {
                        int[] options = program.boardPositions.Where(x => x != 'X' && x != 'O').Select(x => x - '0').ToArray();
                        Random random = new Random();
                        int randomIndex = random.Next(options.Length);
                        playerInput = options[randomIndex];
                    }
                    else
                    {
                        playerInput = Convert.ToInt32(Console.ReadLine());
                    }
                }
                catch
                {
                    Console.WriteLine("Please enter a number.  \nGive it another Try...");
                    continue;
                } 
                if ((playerInput == 1) && (program.boardPositions[0] == '1'))
                    validInputGiven = true;
                else if ((playerInput == 2) && (program.boardPositions[1] == '2'))
                    validInputGiven = true;
                else if ((playerInput == 3) && (program.boardPositions[2] == '3'))
                    validInputGiven = true;
                else if ((playerInput == 4) && (program.boardPositions[3] == '4'))
                    validInputGiven = true;
                else if ((playerInput == 5) && (program.boardPositions[4] == '5'))
                    validInputGiven = true;
                else if ((playerInput == 6) && (program.boardPositions[5] == '6'))
                    validInputGiven = true;
                else if ((playerInput == 7) && (program.boardPositions[6] == '7'))
                    validInputGiven = true;
                else if ((playerInput == 8) && (program.boardPositions[7] == '8'))
                    validInputGiven = true;
                else if ((playerInput == 9) && (program.boardPositions[8] == '9'))
                    validInputGiven = true;
                else
                {
                    Console.WriteLine("Please choose a valid and available board position.  \nGive it another Try...");
                }
            }   

            if (currentTurn == 2)
            {
                program.Play(currentTurn, playerInput);
                currentTurn = 1;
            }
            else if (currentTurn == 1)
            {
                program.Play(currentTurn, playerInput);
                currentTurn = 2;
            }

            program.HorizontalWin();
            program.VerticalWin();
            program.DiagonalWin();
            program.Draw();
        }
    }
}