Chapter 5 exercise 3

Will · September 27th, 2009, 09:30 AM

I am confused about a few things regarding exercise 3 of chapter 5.

The code from the book of application is here:

Code:

namespace ConsoleApplication1
{
    enum orientation : byte
    {
        north = 1,
        east = 2,
        south = 3,
        west = 4,
    }

    struct route
    {
        public orientation direction;
        public double distance;
    }

    class Program
    {
        static void Main(string[] args)
        {
            route myRoute;
            int myDirection = -1;
            double myDistance;
            Console.WriteLine("1) North\n2)East\n3)South\n4) West");
            do
            {
                Console.WriteLine("Select a direction:");
                myDirection = Convert.ToInt32(Console.ReadLine());
            }
            while ((myDirection < 1) || (myDirection > 4));
            Console.WriteLine("Input a distance:");
            myDistance = Convert.ToDouble(Console.ReadLine());
            myRoute.direction = (orientation)myDirection;
            myRoute.distance = myDistance;
            Console.WriteLine("myRoute specifies a direction of {0} and a " +
                "distance of {1}", myRoute.direction, myRoute.distance);
            Console.ReadKey();
        }
    }
}

However the book doesn't explain a few of the things to do with this which I do not understand.

The first part is this line:

Code:

int myDirection = -1;

declaring myDirection as an int and giving it a value of -1, however when I change this number to 0 or 7 or 3 I still get the application to function in the same way. Is this number value an x number?

There is a do while loop in there which acts as validation ensuring that myDirection can only be a value of 1-4 which is why I think that -1 is an x number but I want to check as they don't specify.

Because if it is then shouldn't you just have:

Code:

int myDirection;

as this seems to work as well?

Imar · September 27th, 2009, 01:51 PM

Hi Will,

Take a look at this:

myDirection = Convert.ToInt32(Console.ReadLine());

myDirection is assigned whatever you enter at the console. That means its initial value is never used and as such is indeed useless. -1, 0 (using just int myDirection;) or 7425483 all would have had the same effect.

-1 is often used as a "magic number" to indicate that a value hasn't been set yet. As such, I think this is a preference instead of a necessity.

Cheers,

Imar

Will · September 27th, 2009, 02:41 PM

Cheers Imar,

I was confused because up until this point the book has (I believe) left variables which don't get values until user input as int myDirection; which threw me a bit when I saw -1 as I could not figure out why they would do that.

As you say I can see it makes sense and comes down to personal preference like you say.