Question

I have a code, and I do not understand it. I am developing an application which precision is very important. but it does not important for .NET, why? I don’t know.

double value = 3.5;
MessageBox.Show((value + 1 * Math.Pow(10, -20)).ToString());

but the message box shows: 3.5
Please help me, Thank you.

Answer 1

You can have precision, but it depends on what else you want to do. If you put the following in a Console application:

double a = 1e-20;
Console.WriteLine(" a  = {0}", a);
Console.WriteLine("1+a = {0}", 1+a);

decimal b = 1e-20M;
Console.WriteLine(" b  = {0}", b);
Console.WriteLine("1+b = {0}", 1+b);

You will get

 a  = 1E-20
1+a = 1
 b  = 0,00000000000000000001
1+b = 1,00000000000000000001

But Note that The Pow function, like almost everything in the Math class, only takes doubles:

double Pow(double x, double y);

So you cannot take the Sine of a decimal (other then by converting it to double)

Also see this question.