Can we compute the value of a class property based upon another value of another property of the same class?

Question

I have a class called Person which has properties Name, DateOfBirthand Age. Name and DateOfBirth are supplied when class instance is created but I want the Age property to be computed automatically as soon as the instance of class is created. I know how to do it using Parametrized Constructor but as I am trying to understand the power of Properties, I attempted following program but it is not giving expected output.

using System;

namespace Property
{
    class Person
    {
        #region private varaibles
        private int _age;
        #endregion

        #region properties
        public string Name { get; set; }
        public DateTime DateOfBirth { get; set; }
        public int Age
        {
            get { return _age; }
            set { _age = (DateTime.Now - DateOfBirth).Days / 365; }
        }
        #endregion properties
    }

    class Program
    {
        static void Main(string[] args)
        {
            Person P = new Person() { Name = "Merin Nakarmi", DateOfBirth = new DateTime(1990, 1, 12) };
            Console.WriteLine("{0}, whose Date Of Birth is {1} is {2} years old!", P.Name, P.DateOfBirth, P.Age);    
        }
    }
}

The output I am getting is

I am expecting age to be 28. Help please.

Yes, you need a read-only `Age` property as everyone has noticed. But you have another issue in your code, your `Age` property setter doesn't set the property from the right-hand side of an assignment; I'm surprised it complies. I somehow suspect that if you had assigned 5 to `Age` say: `P.Age=5;` before the WriteLine, then the Age property would have been assigned from `DateOfBirth` and you might have seen 28 and been very confused. Property setters always use the `value` keyword. — Flydog57, Sep 23 '18 at 02:27
As a side note, remember that not every year is 365 days, so you should factor in leap years if you want an accurate age. You can find a solution to that [here](https://stackoverflow.com/questions/9/how-do-i-calculate-someones-age-in-c). — ProgrammingLlama, Sep 23 '18 at 03:00

Hossein · Accepted Answer · 2018-09-23T06:14:09.937

5

It seems you need a readonly age, if that's the case, you don't need to set anything in Age property, simply do:

    public int Age
    {
        get { 
               return DateTime.Now.Year - DateOfBirth.Year;
            }
    }

You may also want to have a look here and read a bit more on properties.
By the way as also @John pointed out concerning the correct calculation of the age(meaning taking leap years into account, you may want to have a look here)

edited Sep 23 '18 at 06:14

answered Sep 23 '18 at 01:39

Hossein

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thi should do it for you – Technivorous Sep 23 '18 at 01:43
@Breeze Am I to conclude from your code that your birthday is on January 1st? – ProgrammingLlama Sep 23 '18 at 02:44
@John: I know your point. the intent here is to show the idea concerning properties only. and I wanted to keep it as simple as possible. – Hossein Sep 23 '18 at 06:01
1

I know :) I was just being pedantic. – ProgrammingLlama Sep 23 '18 at 06:01
I added a note to also have your rightfully correct concern addressed;) – Hossein Sep 23 '18 at 06:16

score 3 · Answer 2 · edited Sep 23 '18 at 01:46

3

You are trying to read the property without setting it. So you can do both of these things in code like

get { return ((DateTime.Now - DateOfBirth).Days / 365); }

edited Sep 23 '18 at 01:46

Hossein

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answered Sep 23 '18 at 01:44

Girish

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Can we compute the value of a class property based upon another value of another property of the same class?

2 Answers2