An example of how to manipulate (insert, delete) an array whilst iterating over it.

looping-and-manipulating.rb

a = [1,2,3,4,5,6]
i = -1

while current = a[i+=1] do 
  prev_one = i==0 ? nil : a[i-1]
  next_one = a[i+1]

  #insert before without iterating over it
  if current == 3 then 
    a.insert i, 2.5
    i+=1
    prev_one = a[i-1]
  end

  #insert after with iterating over it 
  if current == 5 then 
    a.insert i+1, 5.5
    next_one = a[i+1]
  end

  #delete the next one without iterating over it 
  if current == 5.5 then 
    a.delete_at i+1 
    next_one = a[i+1]
  end

  puts "#{prev_one} <<< #{current} >>> #{next_one}"

end

puts "\nResult:"
puts a