How to reverse a chain of characters?

Question

I have to create a program that reverses phrases.

For example: when I write hello guys, I want syug olleh

This is what

Answer 1

Well, of course we want to be able to do this via a constant expression, so we attempt the following:

program reverse
   implicit none
   character(20), parameter :: input = 'Forward'
   integer i
   character(len(input)), parameter :: output = &
      transfer([(input(i:i),i=len_trim(input),1,-1)],trim(input))
   write(*,'("#",a,"#")') input, output
end program reverse

We get the same output with both gfortran and ifort:

#Forward             #
#drawroF#

I can't see what I might be doing wrong... is it the same bug in both compilers?