如何在C＃中声明和显示变量？

Question

I have a class library that has two constructor. The first constructor accepts two arguments and the second accepts three. Below is my class library code. Easier to put the code than try to explain it.

public class Student
    {
        public string name;
        public string course;
        public MyDate bday;

        public Student(string name, string course)
        {
            this.name = name;
            this.course = course;
        }

        public Student(string name, string course, MyDate bday)
        {
            this.name = name;
            this.course = course;
            this.bday = bday;
        }

The MyDate library has another constructor that accepts three arguments which would be the date, month and year of the birthday. Now I have a form which contains 3 listbox and on the third listbox I will be displaying the birthdays. I declare the birthdays in the code (just like i showed below) now I'm having problem on how to display it.

MyDate[] bd = new MyDate[5] {  new MyDate(29, 3, 1990),
                                       new MyDate(30, 1, 1988),
                                       new MyDate(9, 6, 1987),
                                       new MyDate(2, 4, 1989),
                                       new MyDate(17, 8, 1986),
        };
        Student[] s = new Student[5] { new Student("John", "BSCS"),
                                       new Student("Paul", "BSIT"),
                                       new Student("George", "BSCP"),
                                       new Student("Jane", "BSCS"),
                                       new Student("May", "BSIT")
        };

Can anyone please tell me how i should do this? I tried this Student[] s = new Student[5] { new Student("John", "BSCS", bd[0]) and so on but it gives me error. I know this is a beginners question and I am a beginner. Thank you.

Edit: The initialization was done in the form1.cs.

Answer 1

You can see here:

You should set the field initializer under your constructor.

class TestClass
{
    MyDate[] bd;
    Student[] s; 

    public TestClass()
    {
         bd = new MyDate[5] {  new MyDate(29, 3, 1990),
                                   new MyDate(30, 1, 1988),
                                   new MyDate(9, 6, 1987),
                                   new MyDate(2, 4, 1989),
                                   new MyDate(17, 8, 1986),
                            };

         s = new Student[5] { new Student("John", "BSCS"),
                                   new Student("Paul", "BSIT"),
                                   new Student("George", "BSCP"),
                                   new Student("Jane", "BSCS"),
                                   new Student("May", "BSIT")
                             };
    }
}

It's basically saying that you need to set this variable in the constructor.

Answer 2

Based on the error, you're trying to initialize a field (member data) with the another non-static field; you can't do that. The simplest fix is to move your initialization code to the constructor.

So your code would be

partial class Form
{
   MyDate[] bd = ...;
   Student[] s;

   public Form()
   {
      InitializeComponent();

      s = ...;
   }
}

---

You also should chain your Student constructors, and why do you have your own date class instead of using System.DateTime ? You also should use automatic properties rather than public fields.

public class Student
    {
        public string name { get; set; }
        public string course { get; set; }
        public DateTime bday { get; set; }

        public Student(string name, string course)
        {
            this.name = name;
            this.course = course;
        }

        public Student(string name, string course, DateTime bday)
        : this(name, course)
        {
            this.bday = bday;
        }
}

Answer 3

Here's one way to do the same thing:

    Student[] s = new Student[5];
    s[0] = new Student("John", "BSCS", bd[0]);
    s[1] = new Student("Bill", "BSCS", bd[1]);

Answer 4

I must be missing something here, because i am not able to recreate the error discussed here. The following code just works fine for me (.NET 4.0)

public class MyDate
{
    public MyDate(int date, int month, int year)
    {
        this.date = date;
        this.month = month;
        this.year = year;
    }

    public int date;
    public int month;
    public int year;
}

public class Student
{
    public string name;
    public string course;
    public MyDate bday;

    public Student(string name, string course)
    {
        this.name = name;
        this.course = course;
    }

    public Student(string name, string course, MyDate bday)
    {
        this.name = name;
        this.course = course;
        this.bday = bday;
    }
}

..and i am able to initialize the objects like below..

            MyDate[] bd = new MyDate[5]
                          {
                              new MyDate(29, 3, 1990),
                              new MyDate(30, 1, 1988),
                              new MyDate(9, 6, 1987),
                              new MyDate(2, 4, 1989),
                              new MyDate(17, 8, 1986),
                          };

        Student[] s = new Student[5]
                          {
                              new Student("John", "BSCS", bd[0]),
                              new Student("Paul", "BSIT", bd[1]),
                              new Student("George", "BSCP", bd[2]),
                              new Student("Jane", "BSCS", bd[3]),
                              new Student("May", "BSIT", bd[4])
                          };

When exactly are you getting this error?