why (* 1.1 1.1) is 1.2100000000000002 in racket?
racket, scheme
Solution
Oh look, this compares correctly!
> (= (* #e1.1 #e1.1) #e1.21)
#t
(Racket has this really nice feature that `#e1.1` is actually read in as exactly 1.1. Other Scheme implementations do not necessarily work that way, and may actually read in `#e1.1` as floating-point first and then convert to exact.)
Anyway, to elaborate on everybody else's point, without an exactness specifier, Scheme treats a number literal with a dot in it as inexact† (that is, `1.1` and `#i1.1` read in as the same thing). And with inexact numbers, you cannot really expect sane results when doing "exact" comparisons (such as `=`).
† R7RS, section 6.2.5: "If the written representation of a number has no exactness prefix, the constant is inexact if it contains a decimal point or an exponent. Otherwise, it is exact."
Problem
When I try the following in racket: ``` (* 1.1 1.1) ``` why does it return ``` 1.2100000000000002 ``` instead of ``` 1.21 ``` while ``` (* 1.2 1.2) ; is 1.44, as expected ``` Edit and the following returns false: ``` (= (* 1.1 1.1) 1.21); #f ```