add two double given wrong result

Question

I\'m using the following piece of code and under some mysterious circumstances the result of the addition is not as it\'s supposed to be:

double _west = 9.482935         


        

Answer 1

At first I thought this was a rounding error but actually it is your assertion that is wrong. Try adding the entire result of your calculation without any arbitrary rounding on your part.

Try this:

using System;

class Program
{
    static void Main()
    {
        double _west = 9.482935905456543;
        double _off = 0.00000093248155508263153;
        double _lon = _west + _off;

        // check for the expected result
        Console.WriteLine(_lon == 9.48293683793809808263153);       
    }
}

In the future though it is best to use System.Decimal in cases where you need to avoid rounding errors that are usually associated with the System.Single and System.Double types.

That being said, however, this is not the case here. By arbitrarily rounding the number at a given point you are assuming that the type will also round at that same point which is not how it works. Floating point numbers are stored to their maximum representational capacity and only once that threshold has been reached does rounding take place.