Comparing data in Unity

Hi All,

I have a simple enough scenario which is presenting unexpected results.

I am comparing a float with an int multipled with a float. Both the values are equal to 2 but the if statement doesn't think this is the case.

Code (CSharp):

1.     private int leftLane = -1;
2.     private int centreLane = 0;
3.     private int rightLane = 1;
4.     public float laneWidth = 2.0F;
5.  

Later on in the function I move an object towards a lane and want to disable input while this is happening.

Code (CSharp):

1.     bool IsInLane(){
2.         var currentLane = transform.position.x;
3.         if (currentLane == rightLane * laneWidth) {
4.             return true;
5.         }
6.  
7.         return false;
8.     }

You can see from my Immediate window in the debugger that the function should have returned true?
Can anyone explain this to me please?

 

you say currentLane = transform.position.x;
are you snapping this to a grid?

 

No I'm not snapping to a grid. The if statement shoulnd't need to be snapped to anything it should just be comparing two values of type float though?

 

I'm going to guess that it's a precision problem. float*int returns a float, which probably isn't an exact number (eg. 1.00000000001) which in your case will fail the comparison. Just a guess.

 

You should (almost) never test whether two floating point numbers are equal. Instead, test whether they are within some threshold of each other.

So, instead of writing

Code (CSharp):

1. float x, y;
2. // Code
3. if (x == y)

use something like

Code (CSharp):

1. const float epsilon = 1e-5;
2. float x, y;
3. // Code
4. if (Math.Abs(x-y) < epsilon)

 

So I have replaced my compare statement with
Mathf.Approximately()
and it has done the trick.

The problem here wasn't the fact that I shoulnd't have been comparing two floating point numbers, but the fact that the debugger and the immediate window aren't accurate representations of the floats.

Thanks for the help folks