precision in variables

Question

I have problems with the precision of the variables when performing calculations and comparing the results. I am working in C #. Here is an example.

double ImporteDebe;
ImporteDebe = 0;
double base1;
base1 = Convert.ToDouble("10,22");
double PorcentajeIva1;
PorcentajeIva1 = Convert.ToDouble("0,21");
double Iva1;
Iva1 = Convert.ToDouble((base1 * PorcentajeIva1).ToString("N2")); //2,1462 -> 2,15
ImporteDebe = ImporteDebe + base1; // 10,22
ImporteDebe = ImporteDebe + Iva1;// 10,22 + 2,15 = 12,37000000001
if (ImporteDebe == (base1 + Iva1))
{
 System.Diagnostics.Debug.Print(Convert.ToString(ImporteDebe));//condition is never met
}

if you run the code you see that the condition "ImporteDebe == (base1 + Iva1)" is never met

Does the problem have a simple solution?

• Klaus Gütter: Works fine for me; are you sure?
• Guru Stron: works for me.
• TobyB: Try using decimal if double is not specifically required.
• Karlos Garcia: I'm working with Visual Studio 17 and C#. It does not work for me. Condition "ImporteDebe==base1+Iva1" is never satisfied.
• Karlos Garcia: With decimal variables works fine. Use decimal instead of double which implies in relation to executable? Size or speed of execution?

Answer 1

you should not compare doubles using the == operator

but instead like in the official doc here:

// Initialize two doubles with apparently identical values
double double1 = .333333;
double double2 = (double) 1/3;
// Define the tolerance for variation in their values
double difference = Math.Abs(double1 * .00001);
// Compare the values
// The output to the console indicates that the two values are equal
if (Math.Abs(double1 - double2) <= difference)
 Console.WriteLine("double1 and double2 are equal.");
else
 Console.WriteLine("double1 and double2 are unequal.");

• Klaus Gütter: Very good advise in general, but the code in the question should still work as the values on both sides are calculated bit as 10.22 + 2.15
• Natalia Muray: But they might end up slightly different based on the CPU or the compiler used or even the build configuration. This answer is correct