Ruby - What does this code do?

Question

And why output is 1,2,3?

arr = [1,2,3]
puts arr.each{ |x| x = -x}

Answer 1

I'm not sure what exactly you want
if you want the output to be negative.
It should be

arr.each{ |x| puts -x}

not

puts arr.each{ |x| x = -x}