Unexpected question signs in output of example code from Microsoft's page about IFormatProvider.GetFormat(Type)

Question

I was reading about the IFormatProvider.GetFormat(Type) method on Microsoft.com, and decided to run the example code provided on the page.

Instead of this output:

On Monday, the balance of account 10425-456-7890 was $16.34.
On Tuesday, the balance of account 104254567890 was $16.34.

... the program prints out this:

On Monday, the balance of account 10425-456-7890 was 16,34 ?.
On Tuesday, the balance of account 104254567890 was 16,34 ?.

Why are there question marks at the end of each line? I just copied the code into Visual Studio, I did not change anything.

Any hints on how such cases can be debugged? I'm self-studying C# and I don't know much.

The code is:

using System;
using System.Globalization;



namespace ConsoleApp4
{
    public enum DaysOfWeek { Monday = 1, Tuesday = 2 };

    public class AcctNumberFormat : IFormatProvider, ICustomFormatter
    {
        private const int ACCT_LENGTH = 12;

        public object GetFormat(Type formatType)
        {
            if (formatType == typeof(ICustomFormatter))
                return this;
            else
                return null;
        }

        public string Format(string fmt, object arg, IFormatProvider formatProvider)
        {
            // Provide default formatting if arg is not an Int64.
            if (arg.GetType() != typeof(Int64))
                try
                {
                    return HandleOtherFormats(fmt, arg);
                }
                catch (FormatException e)
                {
                    throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
                }

            // Provide default formatting for unsupported format strings.
            string ufmt = fmt.ToUpper(CultureInfo.InvariantCulture);
            if (!(ufmt == "H" || ufmt == "I"))
                try
                {
                    return HandleOtherFormats(fmt, arg);
                }
                catch (FormatException e)
                {
                    throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
                }

            // Convert argument to a string.
            string result = arg.ToString();

            // If account number is less than 12 characters, pad with leading zeroes.
            if (result.Length < ACCT_LENGTH)
                result = result.PadLeft(ACCT_LENGTH, '0');
            // If account number is more than 12 characters, truncate to 12 characters.
            if (result.Length > ACCT_LENGTH)
                result = result.Substring(0, ACCT_LENGTH);

            if (ufmt == "I")                    // Integer-only format.
                return result;
            // Add hyphens for H format specifier.
            else                                         // Hyphenated format.
                return result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8);
        }

        private string HandleOtherFormats(string format, object arg)
        {
            if (arg is IFormattable)
                return ((IFormattable)arg).ToString(format, CultureInfo.CurrentCulture);
            else if (arg != null)
                return arg.ToString();
            else
                return String.Empty;
        }
    }


    public class TestFormatting
    {
        public static void Main()
        {
            long acctNumber;
            double balance;
            DaysOfWeek wday;
            string output;

            acctNumber = 104254567890;
            balance = 16.34;
            wday = DaysOfWeek.Monday;

            output = String.Format(new AcctNumberFormat(),
                                   "On {2}, the balance of account {0:H} was {1:C2}.",
                                   acctNumber, balance, wday);
            Console.WriteLine(output);

            wday = DaysOfWeek.Tuesday;
            output = String.Format(new AcctNumberFormat(),
                                   "On {2}, the balance of account {0:I} was {1:C2}.",
                                   acctNumber, balance, wday);
            Console.WriteLine(output);
        }
    }
    // The example displays the following output:
    //       On Monday, the balance of account 10425-456-7890 was $16.34.
    //       On Tuesday, the balance of account 104254567890 was $16.34.

}