I am new to swift, it's actually my first attempt. I have the following program in playground:
//:===================
import UIKit
func tax(s:Double)->Double{
return s*0.05
}
var xx=66.0*2.0
tax(xx)
//============
The expected result is
6.6,
but swift evaluates the last line as
6.600000000000001
What am I missing.
You are missing nothing. The result comes from the way computers represent numbers. Have a look at this https://en.wikipedia.org/wiki/Floating_point#Accuracy_problems .
If you need perfect numbers and the range is limited you could use Integers and use them premultiplied with a value, for example for a $-value you could just use cent: 145ct instead of 1.45$. This is called fixed point numbers. https://en.wikipedia.org/wiki/Fixed-point_arithmetic
