GRADE CALCULATOR

public static void exit()
        {
            Environment.Exit(0);
        }

        static void Main(string[] args)
        {
            // main

            assign_grade();







            // main //
        }
        static string assign_grade()
        {
            string[] grades = new string[6] { "A", "B+", "B", "C+", "C", "D" };

            int max_score;
            int your_score;
            Console.WriteLine("enter the max score of your test");
            max_score = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine();

            Console.WriteLine("enter your score");
            your_score = Convert.ToInt32(Console.ReadLine());

            if (your_score > max_score)
            {
                Console.WriteLine("Why are you lying, press any key to exit the program");
                Console.ReadKey();
                exit();
            }

            if (your_score >= max_score * 0.9)
            {
                Console.WriteLine("Your grade is: " + grades[0]);
                Console.ReadKey();
                return grades[0];
            }
            if (your_score < max_score * 0.9 && your_score >= max_score * 0.8)
            {
                Console.WriteLine("Your grade is: " + grades[1]);
                Console.ReadKey();
                return grades[1];
            }
            if (your_score < max_score * 0.8 && your_score >= max_score * 0.7)
            {
                Console.WriteLine("Your grade is: " + grades[2]);
                Console.ReadKey();
                return grades[2];
            }
            if (your_score < max_score * 0.7 && your_score >= max_score * 0.6)
            {
                Console.WriteLine("Your grade is: " + grades[3]);
                Console.ReadKey();
                return grades[3];
            }
            if (your_score < max_score * 0.6 && your_score >= max_score * 0.5)
            {
                Console.WriteLine("Your grade is: " + grades[4]);
                Console.ReadKey();
                return grades[4];
            }
            if (your_score <= max_score * 0.5)
            {
                Console.WriteLine("Your grade is: " + grades[5]);
                Console.ReadKey();
                return grades[5];
            }
            else
            {
                Console.WriteLine("Wrong input");
                return null;
            }


        }