Is this the best way to detect negative numbers?

Question

1.00/5 (1 vote)

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Here is my code, I can't really say more to it. I mean, it works fine, but is it really the most effiecient way? It looks so dirt. D:

C#

// -- Distance.
/// <summary>
/// Returns the Pixel distance between two points.
/// </summary>
/// <param name="Entity"></param>
/// <returns></returns>
public int GetDistanceFromEntity(Entity Entity)
{
    /* Return distance. */
    int OurEntityX = this.PositionX.ToString().StartsWith("-") ? -this.PositionX : this.PositionX;
    int OurEntityY = this.PositionY.ToString().StartsWith("-") ? -this.PositionY : this.PositionY;

    int OtherEntityX = Entity.PositionX.ToString().StartsWith("-") ? -Entity.PositionX : Entity.PositionX;
    int OtherEntityY = Entity.PositionY.ToString().StartsWith("-") ? -Entity.PositionY : Entity.PositionY;

    return (int)Math.Sqrt(Math.Pow(OtherEntityX - OurEntityX, 2) + Math.Pow(OtherEntityY - OurEntityY, 2));
}

Posted 20-Feb-13 9:02am

Yvar Birx

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4 solutions

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Matt T Heffron · Accepted Answer · 2013-02-20T09:33:00

Solution 4

This code cannot possibly return the correct distance between two arbitrary points.
If this.PositionX == -2 and Entity.PositionX == +2, the difference between them is 4, but because you are effectively taking the absolute value of each before the subtraction, the difference you get will be 0 (zero!)
For this calculation, just use the .PositionX and .PositionY values AS IS.
The math will all work out!

See the other solutions for answers to the original question...

Posted 20-Feb-13 9:33am

Matt T Heffron

Updated 20-Feb-13 9:34am

v2

Comments

Andreas Gieriet 20-Feb-13 15:46pm

My 5!
See also my solution #2.
Cheers
Andi

Sergey Alexandrovich Kryukov 20-Feb-13 19:16pm

Sure, a 5. (Hard to explain anything to anyone with such "background"; you've done some decent attempt... :-)
—SA

Andreas Gieriet · Accepted Answer · 2013-02-20T09:15:00

I assume your values are int.
There is a function called Math.Abs(...).

[EDIT]
Your function is broken. Coordinates may be in general positive as well as negative (a point may lay in any of the four quadrants[^]). If you take the absolute value of the coordinates before you calculate the coodinate distance results in wrong results. Take the values as they are.

C#

public int GetDistanceFromEntity(Entity Entity)
{
   int deltaX = Entity.PositionX-PositionX;
   int deltaY = Entity.PositionY-PositionY;
   return (int)Math.Sqrt(deltaX*deltaX + deltaY*deltaY);
}

You can test it with points in all quadrants and in both directions:

C#

var q1=new Entity(1, 2);
var q2=new Entity(-3, 2);
var q3=new Entity(-3, -1);
var q4=new Entity(4, -1);
var p0=new Entity(0, 0);

Assert.AreEqual(0, q1.GetDistanceFromEntity(q1), "identiy should have distance 0");
Assert.AreEqual(0, q2.GetDistanceFromEntity(q2), "identiy should have distance 0");
Assert.AreEqual(0, q3.GetDistanceFromEntity(q3), "identiy should have distance 0");
Assert.AreEqual(0, q4.GetDistanceFromEntity(q4), "identiy should have distance 0");
Assert.AreEqual(0, p0.GetDistanceFromEntity(p0), "identiy should have distance 0");

Assert.AreEqual(q2.GetDistanceFromEntity(q1), q1.GetDistanceFromEntity(q2), "distance should be invariant");
Assert.AreEqual(q3.GetDistanceFromEntity(q1), q1.GetDistanceFromEntity(q3), "distance should be invariant");
Assert.AreEqual(q4.GetDistanceFromEntity(q1), q1.GetDistanceFromEntity(q4), "distance should be invariant");
Assert.AreEqual(p0.GetDistanceFromEntity(q1), q1.GetDistanceFromEntity(p0), "distance should be invariant");

Assert.AreEqual(4, q1.GetDistanceFromEntity(q2), "distance q1-q2 mismatch");
Assert.AreEqual(5, q1.GetDistanceFromEntity(q3), "distance q1-q3 mismatch");
...

[/EDIT]

Cheers
Andi

André Kraak · Accepted Answer · 2013-02-20T09:13:00

Solution 1

I think what you are looking for is the Math.Abs Method[^] to always get the positive number.

Posted 20-Feb-13 9:13am

André Kraak

Comments

Yvar Birx 20-Feb-13 15:33pm

Cheers too!

Sergey Alexandrovich Kryukov · Accepted Answer · 2013-02-20T09:16:00

No!!! Stop it immediately! My eyes are hurt. I probably never saw anything worse. Never ever do anything similar. This is the activity opposite to programming, a total abuse.

This is such a weird destructive trend to work with strings representing data instead of data itself. I cannot even explain how wrong it is; it should not happen from the very first steps.

Second thing is: in most cases, you don't even need to tell negatives from positives; arithmetic expressions should correctly work with both. But if you really have to, you should write if (value < 0) {/* ... */}

—SA