The idea is simple. Make a struct for "Departments" of a store, give it a variable for naming (a string called "Department"), and a array to save all buys done in that department.

Now, I want that every time that I'm gonna save a buy on a specific Department, it auto-applies a discount based on department's name and buy amount.

Now, the example class:

class Program
{
    struct Departments
    {
        public string Department;
        private double[] _buys;

        public double[] Buys
        {
            get { return _buys; }
            set
            {
                if (value > 100)
                {
                    if (Department == "CLOTH")
                    _buys = value * .95;
                    if (Department == "FOOD")
                    _buys = value * .90;
                    if (Department == "OTHER")
                    _buys = value * .97;
                }
                _buys = value;
            }
        }
    }

    static void Main()
    {
        var departments = new Departments[3];
        departments[0].Department = "CLOTH";
        departments[1].Department = "FOOD";
        departments[2].Department = "OTHER";
        departments[0].Buys = new double[5];
        departments[0].Buys[0] = 105;
    }
}

Note the line departments[0].Buys[0] = 105, that's the way that I want to save bought things, "Code-Simple"...

Now, note the property Buys of the struct, it's an "Array Property". Then, when I use the value > 100 condition it gives an obvious error, can't cast from double to double[].

The question... how can I write a right condition for value > 100, what else must be put on the stuct to achieve this?

I've tried with "Indexers", but as long as I've tried I can't make it take assignemts via departments[0].Buys[0] = 105 in the right way.

Please note that I wanna keep this schema, specially for the facility of simply say departments[0].Buys[0] = 105 to asing buyings

EDIT:

The previous struct "Departments" is done for example-purposes only. I won't answers about making it by another way to have right "Departments", I want an answer of how to make the set parameter work on individual elements of arrays

• c#
• arrays
• struct
• indexing

One more potential solution is to make another class for the _buys array:

class Buys
{
    private double[] _buys;

    public Buys (int capacity)
    {
        _buys = new double[capacity];
    }

    public double this[int index]
    {
        get { return _buys; }
        set 
        {
            if (value > 100)
            {
                if (Department == "CLOTH")
                    value = value * .95;
                if (Department == "FOOD")
                    value = value * .90;
                if (Department == "OTHER")
                    value = value * .97;
            }
            _buys = value;
        }
    }
}

struct Departments
{
    public string Department;
    public Buys Buys;
}

static void Main()
{
    var departments = new Departments[3];
    departments[0].Department = "CLOTH";
    departments[1].Department = "FOOD";
    departments[2].Department = "OTHER";
    departments[0].Buys = new Buys(5);
    departments[0].Buys[0] = 105;
}

You'd be better off using a List<double> to record the purchases. That way the list can grow dynamically. You can also use indexes to get the list elements.

You can simplify the discount code using a dictionary.

For this data you'd also be better off using a class, rather than a struct. Structs are generally better used for immutable values. Make the class represent a single department and store the appropriate discount in it.

So something like this:

class Program
{
    class Department
    {
        public string Name;
        public double Discount;

        private List<double> _buys = new List<double>();

        public List<double> Buys
        {
            get { return _buys; }
        }

        public void AddBuy(double value)
        {
            _buys.Add(value > 100 ? value * discount : value);
        }
    }

    static void Main()
    {
        var departments = new List<Department>();
        departments.Add(new Department { Name = "CLOTH", Discount = 0.95 });
        departments.Add(new Department { Name = "FOOD", Discount = 0.90 });
        departments.Add(new Department { Name = "OTHER", Discount = 0.97 });
        departments[0].AddBuy(105);

        Console.WriteLine(departments[0].Buys[0]);
    }
}

There are many other ways I'd improve this design, but this should get you going.

you could do something like this

public class Departments
{
    public string Department;
    public MyList buys;
    public Departments()
    {
        buys = new MyList(this, 5);
    }
}
public class MyList
{
    private double[] backingList;
    private Departments owner;
    public MyList(Departments owner, int size)
    {
        this.owner = owner;
        backingList = new T[size];
    }

    public double this[int index]
    {
        get{ return backingList[index]; }
        set { backingList[index] = discountFor(owner.Department) * value; }
    }

    private float discountFor(string department)
    {
        switch(department)
        {
        case "department1":
            return 0.5f;
        //...
        default:
             return 1.0f;
        }
    }

}

However you are not maintaining good separation of concerns by putting the discount into the setter its self. Better code would look something like

departments[0].Buys[0] = DiscountFor("department1") * 105;

By your error you can do something like this.

struct Departments
    {
        public string Department;
        private double[] _buys;
        public double[] Buys
        {
            get { return _buys; }
            set
            {
                for (int i = 0; i < value.Length; i++)
                {
                    if (value[i] > 100)
                    {
                        if (Department == "CLOTH")
                            _buys[i] = value[i] * .95; if (Department == "FOOD")
                            _buys[i] = value[i] * .90; if (Department == "OTHER")
                            _buys[i] = value[i] * .97;
                    }
                }
                _buys = value;
            }
        }
    }

You could create a method to do the setting like this:

        public double[] Buys { get; set; }

        public void SetBuy(int index, double value)
        {
           if (value > 100)
           {
              if (Department == "CLOTH")
               value = value * .95;
              if (Department == "FOOD")
               value = value * .90;
              if (Department == "OTHER")
               value = value * .97;
           }
           _buys[index] = value;
        }

Structs which contain mutable references to mutable items are generally a bad idea, since such structures end up exhibiting a weird combination of value and reference semantics. For example, what should be the effect of:

  Departments dep1,dep2;
  ...
  dep1 = dep2;
  dep1.Department = "CLOTH";
  dep1.Buys[5] = 123;

It's hardly obvious that such a statement will or should affect dep2.Buys[5]. If a given structure's Buys field/property would always refer to the same array, such semantics might be tolerable, but what happens if the array needs to be resized?