c# encapsulation Get/ Set

Question

looking for some clarification on Get / Set. I have this code which I use to create my objects..However I want to have some validation in with the length and width (both need to be greater than some number as example). I believe Get / Set is the way to go and I have used this when changing fields in an instance - but how do I do it at the Instantiation stage?

class Room
{
    public Double dblLength;
    public Double dblWidth;

    public Room (Double _dblLength, Double _dblWidth)
    {

        dblLength = _dblLength;
        dblWidth = _dblWidth;
    }

Answer 1

Turn fields into properties; implement validation within corresponding set:

class Room
{
    private Double m_DblLength;
    private Double m_DblWidth;

    public Room (Double _dblLength, Double _dblWidth) {
      DblLength = _dblLength;
      DblWidth = _dblWidth;
    }

    public Double DblLength {
      get {
        return m_DblLength;
      }
      set {
        //TODO: validation here
        if (value < 0)
          throw new ArgumentOutOfRangeException("value"); 

        m_DblLength = value;
      }
    }

    public Double DblWidth {
      get {
        return m_DblWidth;
      }
      set {
        //TODO: validation here
        if (value < 0)
          throw new ArgumentOutOfRangeException("value"); 

        m_DblWidth = value;
      }
    }