C# Properties - Set question

Question

I'm working in C# and I'm starting to play with properties. One thing I don't know is what is the best way/where to put the logic for the set accessors of class properties and how to handle the errors.

For instance, say I have this (basic) class:

class Person
{
    private int _Age = 18;

    public Person()
    {

    }

    public int Age
    {
        get
        {
            return _Age;
        }
        set
        {
            _Age = value;
        }
    }
}

Now say I have a requirement on the Age property, 0 < Age < 100. Where do I put the logic for this?

Should I put it in the property?

public int Age
    {
        get
        {
            return _Age;
        }
        set
        {
           if (value < 0 || value > 99)
               // handle error
           else
               _Age = Convert.ToInt32(value);
        }
    }

or through class that is creating a Person object?

static void Main(string[] args)
{
   Person him = new Person();
   int NewAge = -10;

   if (NewAge < 0 || NewAge > 100)
      // handle error 
   else
      him.Age = NewAge;
}

Now what if there is a problem with the NewAge (it doesn't meet my constraint)? Should I create a custom exception and throw that? Should I just print a message saying supply a valid age?

I've done some Googling and I cannot find anything that fully answers my questions. I need a book :-/

Answer 1

Use the property setter, it is there for that reason (adding functionality to a field).

If out of range value is passed in, you can throw ArgumentOutOfRangeException or just set it to minimum (or maximum) value, but this depends on your process requirement.