So the objective of this program is very similar to another C# homework problem (practically the same) but I am allowed to use arrays. I still need to set up the last error checking statement, but I wanted to finish and test with what I have so far. I have been working on this for 10+ hours and I am losing confidence every second. I do not know what I am doing wrong; my code always returns as a blank. Please help me point out my mistake so I can fix it. Thank you so much for your help.

 class Program
    {
        static void Main(string[] args)
        {
            char digit1 = ' ', digit2 = ' ', digit3 = ' ', digit4 = ' ', digit5 = ' ', digit6 = ' ', digit7 = ' ';
            int errorCode;

            errorCode = GetInput(ref digit1, ref digit2, ref digit3,
                                 ref digit4, ref digit5, ref digit6, ref digit7);

            errorCode = ProcessInput(ref digit1, ref digit2, ref digit3,
                                     ref digit4, ref digit5, ref digit6, ref digit7);

            ShowResults(ref digit1, ref digit2, ref digit3,
                        ref digit4, ref digit5, ref digit6, ref digit7);

            if (errorCode.Equals(-1))
            {
                Console.WriteLine("ERROR -1: INVALID NUMBER"); //add other error numbers later
            }


            Console.ReadLine();
        }

        static int GetInput(ref char digit1, ref char digit2, ref char digit3,
                            ref char digit4, ref char digit5, ref char digit6, ref char digit7)
        {
            string userInput;
            int errorCode = 0;

            Console.WriteLine("Please enter a seven digit number.");
            userInput = Console.ReadLine();

            if (userInput.Length == 8)
            {
                digit1 = userInput[0];
                digit2 = userInput[1];
                digit3 = userInput[2];
                digit4 = userInput[4];
                digit5 = userInput[5];
                digit6 = userInput[6];
                digit7 = userInput[7];
            }
            else if (userInput.Length != 7)
            {
                errorCode = -1;
            }
            return errorCode;
        }

        static int ProcessInput(ref char digit1, ref char digit2, ref char digit3,
                                ref char digit4, ref char digit5, ref char digit6, ref char digit7)
        {
            int errorCode = 0;

            ToDigit(ref digit1);
            ToDigit(ref digit2);
            ToDigit(ref digit3);
            ToDigit(ref digit4);
            ToDigit(ref digit5);
            ToDigit(ref digit6);
            ToDigit(ref digit7);

            if (digit1 == 5 && digit2 == 5 && digit3 == 5)
            {
                errorCode.Equals(-1);
            }
            else if (digit1 == 0)
            {
                errorCode.Equals(-1);
            }          
            else
            {
                errorCode.Equals(0);
            }

            //if ()    will check for non-alphanumeric numbers
            //{

            //}

            return errorCode;
        }

        static int ToDigit(ref char digit)
        {
            int errorCode = 0;

            switch (digit) //was using a return statement per case, but getting same results.
            {
                case '0':
                    Console.WriteLine('0');
                    errorCode = 0;
                    break;
                case '1':
                    Console.WriteLine('1');
                    errorCode = 0;
                    break;
                case 'a':
                case 'b':
                case 'c':
                    Console.WriteLine('2');
                    errorCode = 0;
                    break;
                case 'd':
                case 'e':
                case 'f':
                    Console.WriteLine('3');
                    errorCode = 0;
                    break;
                case 'g':
                case 'h':
                case 'i':
                    Console.WriteLine('4');
                    errorCode = 0;
                    break;
                case 'j':
                case 'k':
                case 'l':
                    Console.WriteLine('5');
                    errorCode = 0;
                    break;
                case 'm':
                case 'n':
                case 'o':
                    Console.WriteLine('6');
                    errorCode = 0;
                    break;
                case 'p':
                case 'q':
                case 'r':
                case 's':
                    Console.WriteLine('7');
                    errorCode = 0;
                    break;
                case 't':
                case 'u':
                case 'v':
                    Console.WriteLine('8');
                    errorCode = 0;
                    break;
                case 'w':
                case 'x':
                case 'y':
                case 'z':
                    Console.WriteLine('9');
                    errorCode = 0;
                    break;
                default:
                    errorCode = -1;
                    break;
            }

            return errorCode;
        }

        static void ShowResults(ref char digit1, ref char digit2, ref char digit3,
                                ref char digit4, ref char digit5, ref char digit6, ref char digit7)
        {
            char[] digitConvert = new char[8];

            digitConvert[0] = digit1;
            digitConvert[1] = digit2;
            digitConvert[2] = digit3;
            digitConvert[3] = '-';
            digitConvert[4] = digit4;
            digitConvert[5] = digit5;
            digitConvert[6] = digit6;
            digitConvert[7] = digit7;

            string finalNum = new string(digitConvert);
            Console.WriteLine(finalNum.ToUpper());
        }
    }

The only problem I had with this code is that you ask for a seven digit number to be input but your check in GetInput looks for whether the input string is of length 8, not 7.
Enter an 8 digit number and everything works just fine.

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