CODEWITHSUNDEEP
c#sumdivision
Christopher
Christopher

Reputation: 2057

Division using Sum does not work

In my program, I created a list of a custom class. This class contains a integer property. I want to divide an other given integer by the sum of these properties in my list - but Sum() does not seam to work properly in divisions.

I created a short demo for you, it's a simple console application:

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

namespace Sum
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Class> list = new List<Class>() {
                new Class() { Property = 1},
                new Class() { Property = 1},
                new Class() { Property = 1},
                new Class() { Property = 1},
                new Class() { Property = 1},
                new Class() { Property = 1}
            };

            Console.WriteLine("Sum: " + list.Sum(x => x.Property));
            Console.WriteLine("Division: " + (2 / list.Sum(x => x.Property)));
            Console.ReadLine();
        }
    }

    public class Class
    {
        public int Property { get; set; }
    }
}

I know that I could save the sum of the properties in a new variable and use it afterwards for my division. But shouldn't Sum should work successful in this situation?

Upvotes: 0

Views: 815

Answers (5)

cuongle
cuongle

Reputation: 75316

Sum actually work, but result is 0 because you use integer division: int divides int => result will be int, you should change:

(2.0 / list.Sum(x => x.Property))

It will work

Upvotes: 2

p.s.w.g
p.s.w.g

Reputation: 149040

That's because you're using integer division, not floating-point division. Try using 2f instead to a float constant:

Console.WriteLine("Division: " + (2f / list.Sum(x => x.Property)));

Or 2d instead to a double constant:

Console.WriteLine("Division: " + (2d / list.Sum(x => x.Property)));

Or 2m instead to a decimal constant:

Console.WriteLine("Division: " + (2m / list.Sum(x => x.Property)));

Any one will give you the result you're looking for (with only some difference in accuracy)

Upvotes: 2

Tim Schmelter
Tim Schmelter

Reputation: 460208

I assume that you expect the result to be 2 / 6 = 0,33 but integer division always result in an integer (in C#). So at least one number must be a floating point type like double.

Console.WriteLine("Division: " + (2d / list.Sum(x => x.Property)));

The division rounds the result towards zero, and the absolute value of the result is the largest possible integer that is less than the absolute value of the quotient of the two operands. The result is zero or positive when the two operands have the same sign and zero or negative when the two operands have opposite signs.

http://msdn.microsoft.com/en-us/library/aa691373(v=vs.71).aspx

Upvotes: 2

user1300630
user1300630

Reputation:

I think it will write 0 to the output, because of the integer division.

Upvotes: 0

JaredPar
JaredPar

Reputation: 755141

The problem here is you are using integer division which supports whole numbers only. You want instead to do floating point division which supports decimals 

Console.WriteLine("Division: " + ((double)2 / list.Sum(x => x.Property)));

Upvotes: 4

Related Questions