Question

I need to add a private reference to a Unit object _Unit. Attached is both classes (Unit and Result).

I understand I need to have the code below, however it results in errors (listed below):

// 14. create new class
class Result : Unit

and the below creates the error that base() requires two constructors:

// 17. Create constructor for the class
public Result(string grade, Unit _Unit) : base(_Unit)

In my unit class there are two private strings _Code and _Name. Please ask if you need any other class codes put in or the assignment question.

namespace SIT232_Assignment1
{
  // 14. create new class
  class Result
  {
    // 15. Add a private reference to a Unit objectand a private string attributes.
    private string _Grade, _Unit;

    // 16. Encapsulate the above attributes with public read-only properties
    public string Grade
    {
        get { return _Grade; }            
    }

    // 17. Create constructor for the class
    public Result(string grade, Unit _Unit) 
    {            
        _Grade = grade;            
    }

    // 18. create a public read-only property of type bool
    public bool Passed (string grade)
    {
        bool result = true;
        if (_Grade == "N")
            result = false;
        return result;
    }

    // 19. Create a public static methods 
    public static bool ValidateGrade(string grade)
    {
        bool result = false;
        if (_Grade == "N" || _Grade == "P" || _Grade == "C" || _Grade == "D" || _Grade =="HD")
            result = true;
        return result;            
    }

    // 20. Define a ToString method
    public override string ToString()
    {
        return String.Format("{0}\t{1}", _Grade);
    }
}

namespace SIT232_Assignment1
{
  // 8. Create new class
  class Unit
  {
    // 9. Add private string attributes for the unit code and unit name
    private string _Code, _Name;

    // 10. Encapsulate the above attributes with public read-only properties.
    public string Code
    {
        get { return _Code; }            
    }                
    public string Name
    {
        get { return _Name; }            
    }     

    // 11. Create constructor with two string parameters
    public Unit( string code, string name)
    {
        _Code = code;
        _Name = name;
    }

    // 27. create a private list<>
    private List<Student> _EnrolledStudents = new List<Student>();

    // 28. Encapsulate the above list with read-only
    public ReadOnlyCollection<Student> EnrolledStudents
    {
        get { return _EnrolledStudents.AsReadOnly(); }
    }

    // 29. Create a method that accecpts a single parameter
    public void RecordEnrollment(Student student)
    {
        _EnrolledStudents.Add(student);
    }

    // 30. Create a method that accecpts a single parameter
    public void RemoveEnrollment(Student student)
    {
        _EnrolledStudents.Remove(student);
    }

    // 12. Define a ToString method
    public override string ToString()
    {
        return String.Format("{0} {1}", _Code, _Name);
    }
}

Furthermore, one other error I’m getting that I simply cannot full understand is the below method HAS to be static, I’ve researched that also making the attributes and properties of _Grade static solves the error showing on each individual _Grade, however it still shows on the first one?

if (_Grade == "N" || _Grade == "P" || _Grade == "C" || _Grade == "D" || _Grade =="HD")

public static bool ValidateGrade(string grade)

Answer 1

For your first question:

Your class Result inherites from Unit and your constructor of Result calls the one of the base class. However, in Unit there is only one constructor defined needing two arguments (code and name), so your call to base at the Result constructor needs to have two parameters.

But you probably don’t want to inherit from Unit but add a private reference to it. There you would have something like

class Result {

  private Unit _Unit;

  ...

  public Result(..., Unit _Unit)
  {
      this._Unit = _Unit;
      ...
  }
}

Your second error: A static method can only access static fields and properties, so from a static method you can’t access your instance variables. You just want to verify that the supplied grade is in your range, so just dont refer to the instance variable_Grade`:

public static bool ValidateGrade(string grade)
{
  return (grade == "N" || grade == "P" ...)
}