VARCHECK_NEW UPDATE W/ SWICTH 001

    class Program
    {

        static void Main(string[] args)
        {
            Console.Write("Input Variable: ");
             string variable = Console.ReadLine();
             char[] cha = variable.ToCharArray();

            int state = 0;

            for (int i = 0; i <= cha.Length-1 ; i++)
            {
                char ch = cha[i];

                switch (state)
                {
                    case 0:
                        {
                            if (!(ch < 64 || ch > 91) || (ch == 95) || !(ch < 97 || ch > 123))
                            {

                                state = 1;
                                if (i == cha.Length - 1)
                                    goto case 3;
                            }
                            else
                                goto default;

                            break;
                        }
                    case 1:
                        {
                            if (i == cha.Length - 1)
                            {
                                goto case 2;
                            }
                            else
                            {
                                if (!(ch < 48 || ch > 57) || !(ch < 65 || ch > 91) || (ch == 95) || !(ch < 97 || ch > 123))
                                {

                                    state = 2;
                                }
                                else
                                    goto default;
                            }
                            break;
                        }
                    case 2:
                        {
                            if (!(ch < 48 || ch > 57) || !(ch < 65 || ch > 91) || (ch == 95) || !(ch < 97 || ch > 123))
                            {
                                    goto case 3;
                            }
                            else
                                goto default;
                        }
                    case 3:
                        {
                            Console.WriteLine("success");
                            return;
                        }
                    default:
                        {
                            Console.WriteLine(" Oooppss ...Invalid!!!");
                            return;
                        }
                }
            }

      //coded by elamigo-JGT ACT CS STUDENTS
            }
        }
    }