ConsoleAppTest01.cs

using System;

namespace ConsoleAppTest01
{
    class Program
    {
        static readonly Random RNG = new Random();

        enum Choice
        {
            Invalid = -1,
            Rock,
            Paper,
            Scissors
        }

        enum State
        {
            Win = 0,
            Loss,
            Draw
        }

        static State Check(Choice user, Choice ai)
        {
            if (user == Choice.Rock)
            {
                if (ai == Choice.Paper) return State.Loss;
                else if (ai == Choice.Scissors) return State.Win;
            }
            else if (user == Choice.Paper)
            {
                if (ai == Choice.Rock) return State.Win;
                else if (ai == Choice.Scissors) return State.Loss;
            }
            else if (user == Choice.Scissors)
            {
                if (ai == Choice.Rock) return State.Loss;
                else if (ai == Choice.Paper) return State.Win;
            }

            return State.Draw;
        }

        static Choice ProcessInput(string input)
        {
            string proc = input.ToLower().Trim();

            if (proc == "rock") return Choice.Rock;
            else if (proc == "paper") return Choice.Paper;
            else if (proc == "scissors") return Choice.Scissors;
            else return Choice.Invalid;
        }

        static Choice RandomChoice()
        {
            int rand = RNG.Next(300);

            if (rand <= 100) return Choice.Rock;
            else if (rand <= 200) return Choice.Paper;
            else return Choice.Scissors;
        }

        static void Main(string[] args)
        {
            string input = String.Empty;
            State results;
            Choice user, ai;
            int wins = 0, losses = 0;

            Console.WriteLine("Let's play a simple game of Rock, Paper, Scissors!");
            Console.WriteLine("When you're done, simply input 'quit' or close this window!");

            while (input != "quit")
            {
                Console.Write("Pick a choice between rock, paper and scissors: ");
                input = Console.ReadLine();

                user = ProcessInput(input);
                ai = RandomChoice();
                results = Check(user, ai);

                if (user == Choice.Invalid)
                {
                    Console.WriteLine("Come on now, that's not a valid option...");
                    continue;
                }

                Console.WriteLine("You chose {0} while the computer chose {1}...", user, ai);

                if (results == State.Win)
                {
                    Console.WriteLine("You won!");
                    wins++;
                }
                else if (results == State.Loss)
                {
                    Console.WriteLine("The computer won!");
                    losses++;
                }
                else
                {
                    Console.WriteLine("It's a draw! Nobody wins.");
                }

                Console.WriteLine("That puts it at {0} for you and {1} for the computer. How about a rematch?", wins, losses);
            }

            Console.WriteLine("Done already? Alright, see you later!");
            Console.Write("Press any key to close this window.");
            Console.ReadKey();
        }
    }
}