Question

I’ve recently started trying to teach myself C# and this is very much a beginner’s attempt at the implementation of using business rules in a property, in my case the FurColor. When I run the program below I get a NullReferenceException. Can someone help me find the cause of this error? The exception occurs at line 15

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

namespace _10_23_Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("programming practice!");
            Dog d = new Dog();
            Console.Write("what color is your dog: ");
            d.FurColor = Console.ReadLine();
            Console.WriteLine("the color of your dog is {0}", d.FurColor);
        }
    }
    class Dog
    {
        private string furColor;
        private string petName;
        private int tagNum;

        public Dog() { }

        public Dog(string color, string name, int tagID)
        {
            furColor = color;
            petName = name;
            tagNum = tagID;
        }
        //properties
        public string FurColor
        {
            get { return furColor; }
            set {                    
                    do
                    {
                        Console.Write("enter in a viable color type: ");
                    }
                    while (furColor.Length > 10);
                    furColor = value;
                }
        }
        public string Name
        {
            get { return petName; }
            set { petName = value; }
        }
        public int TagNum
        {
            get { return tagNum; }
            set { tagNum = value; }
        }

    }
}

Answer 1

Once corrected you will get an infinite loop though.

Side note : You should not ask for input in the Set clause of your property.

You should prefer a member function that would ask for the input, check if it’s valid and then set the color.

In you dog class add a function that looks like this :

public void setFurColor()
{
    string color = string.Empty;
    do
    {
        Console.Write("what color is your dog: ");
        color = Console.ReadLine();
    }while ( ! string.IsNullOrEmpty(color)  && bleh.Length < 10);
    this.furColor = color;
}