Person

using System;
namespace Person
{
    /*
     * Task 4
     * Create a class Person with two fields – name and age.
     * Age can be left unspecified (may contain null value.
     * Override ToString() to display the information of a person and if age is not specified – to say so.
     * Write a program to test this functionality.
     */

    public class Person
    {
        //Fields
        private string name;
        private int? age;
        //Constructors
        public Person(string name)
        {
            this.Name = name;
        }
        public Person(string name, int? age)
            : this(name)
        {
            this.Age = age;
        }
        //Properties
        public string Name
        {
            get { return name; }
            set
            {
                if (string.IsNullOrEmpty(value))
                {
                    throw new ArgumentException("A Person must have a name!");
                }
                name = value;
            }
        }
        public int? Age
        {
            get { return age; }
            set
            {
                if (value < 0 || value > 150)
                {
                    throw new ArgumentException(" This is not a possible human age!");
                }
                age = value;
            }
        }
        //Methods
        public override string ToString()
        {
            if (this.age == null)
            {
                return string.Format("Person name is: {0} , age unknown.", this.Name);
            }
            else
            {
                return string.Format("Person name is: {0} , age {1}.", this.Name, this.Age);
            }
        }
    }

    //Test person class
    public class TestPerson
    {
        public static void Main()
        {
            Person johny = new Person("Johny");
            Console.WriteLine(johny);
            johny.Age = 54;
            Console.WriteLine(johny);
            johny.Age = null;
            Console.WriteLine(johny);
        }
    }
}