reverse_string.rb

# variants reverse string in ruby
# first variant
s = "string".split(//)
sl = s.size - 1
for i in s 
  print s[sl]
  sl -= 1 
end

# second (primary)
s = "string"
middle_i = s.length / 2 - 1
(0..middle_i).each { |i| s[i], s[-i-1] = s[-i-1], s[i] }

# third (only numbers)
s = [1, 2, 3, 7, 8, 9]
middle_i = s.length / 2 - 1
(0..middle_i).each do |i|
  s[i] = s[-i-1] ^ s[i]
  s[-i-1] = s[-i-1] ^ s[i]
  s[i] = s[-i-1] ^ s[i]
end