Using objects from one class in another class

Question

I have two classes Teacher and Student. I am trying to get teacher to use the class functions in students. The problem I am having is that I need the number of student object being used in Teacher to be random. I thought I figured this out in the constructor, but I had to declare new student object in every function of teacher that I use student. So that just creates a new student object which does me no good. Here is my code

class Teacher
{
    private bool absence;
    private bool level;
    private static int uniqueID = 0;
    private ArrayList arrayList = new ArrayList();
    private ArrayList arrayList1 = new ArrayList();
    private int id = 0;
    private int numPages;
    private char present;
    Random random = new Random();
    int randomLevel = random.Next(20, 30);//this line does not work, if I could then I would just use randomLevel in the in the line below for creating my student objects
    Student student = new Student();
    int maybe;

    public Teacher()
    {
        int randomLevel = random.Next(1, 3);
        id = uniqueID;
        absence = false;
        level = (randomLevel % 2 == 0);
        uniqueID++;
        randomLevel = random.Next(20, 30);
        Student[] student = new Student[randomLevel];
        maybe = randomLevel;
        for (int i = 0; i < randomLevel; i++)
        {
            student[i] = new Student();
        }
    }

and here is a function in teacher that uses student

  public void addPages()//Come back need to add specific child
  {
        int choice = 0;
        Console.WriteLine("Enter the student ID");
        choice = int.Parse(Console.ReadLine());
        Student[] student= new Student[maybe];//If i get rid of this line then how will I choose which student object to use.  However this created a new student object and I do not want to do that

        student[choice] = new Student();
        int number = 0;
        if (student[choice].absent())
        {
            number = student[choice].excused();
        }
        else
        {

            Console.WriteLine("How many pages did the student read today? ");
            number = int.Parse(Console.ReadLine());
        }
        student[choice].add(number);           
   }

Is there a way to get the random to work in the declaration area above the constructor?

just declare a class instance variable Students like the others you already have — BrokenGlass
– BrokenGlass, Commented Jan 18, 2012 at 21:03
@JuanCarlosVegaNeira: baby steps here. This looks like a 100-level C# class and an early exercise at that. — Austin Salonen
– Austin Salonen, Commented Jan 18, 2012 at 21:06

Austin Salonen · Accepted Answer · 2012-01-18 21:03:43Z

3

I think your problem comes down to variable scope but you have provided quite a bit of extraneous code. I'll simplify down to what I think you actually care about.

class Teacher
{
    // class-level list of students
    private List<Student> _students = new List<Student>();

    public Teacher()
    {
        var random = new Random();
        var studentCount = random.Next(20,30);

        for(int i = 0; i < studentCount; i++)
        {
            _students.Add(new Student());
        }
    }

    // use _students from here on out
    public void AddPages(...) { ... }
}

answered Jan 18, 2012 at 21:03

Austin Salonen

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Comments

Charles Lambert · Accepted Answer · 2012-01-18 21:01:35Z

1

You cannot initialize a field with a function call outside of a constructor or method. Also you should promote the student array you created in your constructor to a field of your class. That way you can access the student array in your addPages method.

answered Jan 18, 2012 at 21:01

Charles Lambert

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Comments

phoog · Accepted Answer · 2012-01-19 00:19:59Z

Is there a way to get the random to work in the declaration area above the constructor?

No. You will have to make that call in the constructor itself.

There are many other problems with your code, which seems confused. It's difficult to suggest the best approach, since you haven't listed your requirements in detail.

One of the clearest signs of confusion in your code is that each method declares a local variable that hides the field student:

Student[] student = new Student[randomLevel];

and

Student[] student = new Student[maybe];

Another sign of confusion is that the locals are not of the same type as the field. The locals are arrays of type Student[], while the hidden field is just a single student:

Student student = new Student();

This is a great example of why it's a good idea to use plural names for arrays and collections. It's confusing if you call the contents of a library by the name book rather than books. It's also a good example of the value of having a distinct naming convention for fields, like the common approach of using an underscore prefix (although some people disagree with the practice). This makes it easy to keep fields and local variables separate in your thinking.

Since you want the teacher object to have a collection of student objects on which to operate, and you want that collection to persist across method calls, the collection should be a field of the Teacher class, as Austin Salonen suggests. (In general, as Austin implies, most people prefer the generic List<> over arrays, for several reasons. I'll leave that question aside for now, since you're probably using arrays for pedagogical reasons.)

When you're picking a student for a specific operation, you select the student by index:

int index = GetIndexFromUserOrWhereverElse();
Student student = _students[index];
DoSomethingWith(student);

If you want to do the same thing to each of the students, you can use a for loop or a foreach loop:

for (int index = 0; index < students.Length; index++)
    DoSomethingTo(_students[index]);

or

foreach(Student student in _students)
    DoSomethingTo(student);

Another suggestion: Use descriptive names for your variables and methods:

The name number is not descriptive.
It's not clear why the excused() method returns an integer.
It's not clear what it means to add() an integer to a student, especially since if you add the number for an absent student, the value comes from the excused() method, and otherwise it represents a number of pages entered by the user.

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