NUnit??? 2

[ajikoe]

Hello I use NUnit for testing, but I found something wierd:

Assert.AreEqual(0.1,Math.Abs(2.1-2));//TRUE
Assert.AreEqual(true,Math.Abs(2.1-2)==0.1);//FALSE

Can anyone explain it?

Sincerely Yours,
Pujo

 

[chiph]

0.1 cannot be precisely represented in floating point (remember, everything is stored internally as binary), so you always get rounding errors. So comparing exact floating-point values will occasionally give you results like this.

I haven't seen any perfect way of handling this -- primarily, you should try not to floating point comparisons using the equality operator.

One method would be to decide on a level of accuracy, and test the value to see if you're within that range.

float Tolerance = 0.001;
float Value1 = 0.1;
float Value2 = 0.1;

if ((Value1 + Tolerance > Value2) && (Value1 - Tolerance < Value2))
{
   // Value1 is close enough to call it being equal
   // to Value2
}

Chip H.


____________________________________________________________________
If you want to get the best response to a question, please read FAQ222-2244 first

 

[cappmgr]

Same result just a little different

float Tolerance = 000.1f;
float Float1 = 0.1f;
float Float2 = 0.1f;
if (Math.Abs(Float1 - Float2) > Tolerance)
{
    Console.WriteLine("not equal");
}

Marty

 

[obislavu]

You can apply the solutions recommended in the above posts but you should use Single.Epsilon , Double.Epsilon in such cases.
In the example below you will see the action of the Epsilon:

{
		float x1=(float)1/3;
		float x2=(float)0.33333333333;
		if (Math.Abs(x1-x2)<Single.Epsilon)
		{
			Console.WriteLine("Float Are equal");
		}
		else
		{
			Console.WriteLine("Float Are not equal");
		}
	}
	{
		double x1=(double)1/3;
		double x2=(double)0.33333333333;
		if (Math.Abs(x1-x2)<Double.Epsilon)
		{
			Console.WriteLine("Double Are equal");
		}
		else
		{
			Console.WriteLine("Double Are not equal");
		}
	}

The results are:
Float Are equal
Double Are not equal
obislavu

 

[chiph]

Thanks, obislavu. I had forgotten about that static constant.

Chip H.


____________________________________________________________________
If you want to get the best response to a question, please read FAQ222-2244 first

 

[ajikoe]

thanks everyone