Array, Arraylist or list of lists?

Question

I was going to use a standard array, I need it to x number of rows and be 2 columns

double[,] members = new double[x, 2];

and loop through all the results I get back and then add them to the array, but as the number of results can change I don't want to pre-define the size of the array...

members[0, 0] = cost;
members[x, 1] = tax;
x++;

I was looking at resizing the array but would it be easier just using an arraylist or list of lists for this?

Answer 1

I would have a list of some type, where that type has a cost and a tax.

If space is a premium, it could be a struct with two doubles (btw, would decimal be more appropriate? It is almost always is a better choice for money), but if so: make it immutable.

For example:

public struct YourType {
    private readonly decimal cost, tax;
    public decimal Cost { get { return cost; } }
    public decimal Tax { get { return tax; } }
    public YourType(decimal cost, decimal tax) {
        this.cost = cost;
        this.tax = tax;
    }
}

With:

List<YourType> list = new List<YourType>();

Answer 2

Perhaps the number of items in the second dimension is fixed, or at least, is predictable, so if you're using Microsoft .NET Framework 4.0, you can use a list of tuples:

List<Tuple<double, double>> list = new List<Tuple<int, int>>();

// In your loop...
list.Add(Tuple.Create(cost, tax));

// ... later when retrieving some tuple...
int item0cost = list[0].Item1;
int item0tax = list[0].Item2;

You can always implement some kind of value object class which has Cost and Tax properties, but using tuples you can do it as easy as I shown you in my code sample.