Csharp ID check

        private bool checkID(string inputStr)
        {
            int[] alphabetValueArray = {
                10, 11, 12, 13, 14, 15, 16, 17,
                34, 18, 19, 20, 21, 22, 35, 23,
                24, 25, 26, 27, 28, 29, 32, 30,
                31, 33 };
            int[] weightArray = { 1, 9, 8, 7, 6, 5, 4, 3, 2, 1, 1 };
            if (inputStr.Length != 10) {
                return false;
            }
            int checkValue = 0;
            char[] inputCharArray = inputStr.ToUpper().ToCharArray();
            if (inputCharArray[0] < 'A' || inputCharArray[0] > 'Z') {
                return false;
            }
            int alphabetValue = alphabetValueArray[inputCharArray[0]-'A'];
            checkValue = (alphabetValue / 10) * weightArray[0] + (alphabetValue % 10) * weightArray[1];
            for (int i=1; i<10; i++) {
                if (inputCharArray[i] < '0' || inputCharArray[i] > '9') {
                    return false;
                }
                int charValue = inputCharArray[i] - '0';
                checkValue += charValue * weightArray[i+1];
            }

            if (0 == (checkValue % 10)) {
                return true;
            } else {
                return false;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show("Result: " + checkID(textBox1.Text).ToString());
        }