Csharp try 创建一个C#程序，该程序使用自动实现的属性、覆盖ToString()并使用子类

• 自动实现的属性:您已经正确地为Letter类中的Name和DateMailed实现了自动实现的属性.您将希望对CerfiedLetter类中的TrackingNumber执行类似的操作.

• 认证信函类:认证信函应该继承自信函，并为跟踪编号添加一个额外的属性.TrackingNumber不应该是方法，而应该是属性.您可以在CerfiedLetter的构造函数中生成跟踪编号.

• 处理认证信件:在Main方法中，当用户指示信件经过认证时，需要创建CertifiedLetter的实例.此实例还应该有一个名称和日期，以及跟踪编号.

• CertifiedLetter中的ToString方法:重写CertifiedLetter中的ToString方法以包括有关跟踪编号的信息.

例如如下所示:

class LetterDemo
{
    static void Main()
    {
        WriteLine("Please enter name of recipient >> ");
        string inputName = ReadLine();

        WriteLine("Please enter the date letter was mailed >> ");
        string inputDate = ReadLine();

        WriteLine("Is letter certified? Y or N >> ");
        string isCertified = ReadLine();

        Letter letter;

        if (isCertified.Equals("Y", StringComparison.OrdinalIgnoreCase))
        {
            letter = new CertifiedLetter
            {
                Name = inputName,
                DateMailed = inputDate
            };
        }
        else
        {
            letter = new Letter
            {
                Name = inputName,
                DateMailed = inputDate
            };
        }

        WriteLine(letter.ToString());
    }
}

class Letter
{
    public string Name { get; set; }
    public string DateMailed { get; set; }

    public override string ToString()
    {
        return GetType().Name + " is being sent to " + Name + " on the day of " + DateMailed + ".";
    }
}

class CertifiedLetter : Letter
{
    public int TrackingNumber { get; }

    public CertifiedLetter()
    {
        Random rnd = new Random();
        TrackingNumber = rnd.Next(1000, 9999);
    }

    public override string ToString()
    {
        return base.ToString() + " The tracking number is " + TrackingNumber + ".";
    }
}

根据您的 comments 进行编辑:

您可以更直接地打印字母属性:

static void Main()
{
    WriteLine("Please enter name of recipient >> ");
    string inputName = ReadLine();

    WriteLine("Please enter the date letter was mailed >> ");
    string inputDate = ReadLine();

    WriteLine("Is letter certified? Y or N >> ");
    string isCertified = ReadLine();

    if (isCertified.Equals("Y", StringComparison.OrdinalIgnoreCase))
    {
        // Create and display a CertifiedLetter
        CertifiedLetter certifiedLetter = new CertifiedLetter
        {
            Name = inputName,
            DateMailed = inputDate
        };
        WriteLine(certifiedLetter.ToString());
    }
    else
    {
        // Create and display a regular Letter
        Letter letter = new Letter
        {
            Name = inputName,
            DateMailed = inputDate
        };
        WriteLine(letter.ToString());
    }
}