Question

Currently I am writing my thesis and I was confronted with a behavior of .Net C# that I had never seen before. I am talking about an error in a calculation.
I implemented this formula:

1/2 * (Theta i-1 + Theta i) + Sum(Alph k, k=1, i-1)

This formula is applied to 4 objects. Theta is in all objects declared as float with the value 1,5708. Alpha is initialized with 0 and will be increased by each iteration.

First implmentation

    float alpha = 0;
    float value = 0;
    for (int sphereCount = 1; sphereCount < this.spheres.Count; sphereCount++)
    {
        value = (1/2) * (this.spheres[sphereCount - 1].Theta + this.spheres[sphereCount].Theta);
        alpha += value;
    }

With this version value is always 0.0!
So I changed it to:

Working implementaion

    float alpha = 0;
    float value = 0;
    for (int sphereCount = 1; sphereCount < this.spheres.Count; sphereCount++)
    {
        value =(this.spheres[sphereCount - 1].Theta + this.spheres[sphereCount].Theta) * 1/2;
        alpha += value;
    }

By removing the brackets around the 1/2 and placing it at the end of the calculation it worked.

WHY IS THAT SO???

It seems when you place 1/2 in brackets not depending on the position of 1/2 the result is 0.0. But also when i place (1/2) at the end it results in 0.0.
Does anyone here have an idea why?

Answer 1

This

(1 / 2)

evaluates to 0 because it’s integer division. If you say

(1 / 2f)

or

(1 / (float) 2)

you’ll be fine because it forces float divsion. Or, even better, just write 0.5.