числителни редни имена

OrdinalNumbers.cs

public class OrdinalNumbers
{
    public static string GetOrdinal(int number)
        => $"{number}{GetOrdinalSuffix(number)}";

    public static string GetOrdinalSuffix(int number)
        => number < 0
            ? ""
            : (number % 100) switch
            {
                0 => "",
                11 or 12 or 17 or 18 => "ти",
                int n =>
                    (n % 10) switch
                    {
                        1 => "ви",
                        2 => "ри",
                        7 or 8 => "ми",
                        _ => "ти",
                    }
            };
}