nullableUsage

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MobilePhoneDevice
{
    class Battery
    {
        private string model;
        private double? hoursIdle = 4d;  // !
        private double? hoursTalk = 0.5d; // !
        public BatteryType BatteryType { get; set; }

        //property for model
        public string Model
        {
            get
            {
                return this.model;
            }
            private set // ????
            {
                this.model = value;
            }
        }

        //property for hours idle
        public double? HoursIdle
        {
            get { return this.hoursIdle; }
            private set // ????
            {
                if (value==null)
                {
                    this.hoursIdle= hoursIdle;
                }
            }
        }

        //property for hours talk
        public double? HoursTalk
        {
            get { return this.hoursTalk; }
            private set // ????
            {
                if (value==null)
                {
                    this.hoursTalk = hoursTalk;
                }
            }
        }

        //no default contructor
        //public Battery()
        //{
        //}

        //constructor
        public Battery(string model):this(model, null,null,BatteryType.Liion)
        {

        }

        //constructor
        //public Battery(string model, double hoursTalk):this(model,null,hoursTalk,BatteryType.Liion)
        //{
        //}
        //constructor
        public Battery(string model, double? hoursIdle, double? hoursTalk,BatteryType batteryType)
        {
            this.model = model;
            this.HoursIdle = hoursIdle;
            if (hoursIdle<0)
            {
                throw new ArgumentException();
            }
            this.HoursTalk = hoursTalk;
            if (hoursTalk<0)
            {
                throw new ArgumentException();
            }
            this.BatteryType = batteryType;
        }
        static void Main()
        {

            Battery battery = new Battery("varta");
            Console.WriteLine(battery.model);
            Console.WriteLine(battery.HoursIdle);
            Console.WriteLine(battery.hoursTalk);
        }
    }
}