How can I convert float(-1.0) to int -1 correctly?

Question

my code:

step := 10.0
precision := int(math.Log10(1/step))
fmt.PrintLn(precision)

I want precision == -1 but got 0...

Answer 1

Float to integer conversion truncates, so if your float number is e.g. 0.99, converting it to integer will be 0 and not 1.

If you want to round to an integer, you may simply use math.Round() (which returns float64 so you still need to manually convert to int, but the result will be what you expect):

step := 10.0
precision := int(math.Log10(1 / step))
fmt.Println(precision)

precision = int(math.Round(math.Log10(1 / step)))
fmt.Println(precision)

This will output (try it on the Go Playground):

0
-1

If you want to round to a specific fraction (and not to integer), see Golang Round to Nearest 0.05.