Ruby: airline reservation (arrays)

[Hugg]

I cannot, for the life of me and my goldfish, get this code to work for an assignment. I cannot make it change the array location to a 1 to make it "filled" by a passenger. I do .inspect at the end of the script and the array is just full of 0's (like how it is already set up), nothing I have tried will get the array to reflect what I want it to do.

What am I doing wrong?

The boolean array is called $assignment. Coach is $c and First class is $f. $i is the counter to keep track of where the 0's and 1's are in the array (I think, at least that's what I want it to do). First class is seats 1-5 and Coach is 6-20.

loop do
    puts "If you'd like to fly in first class, Press [1]. If you'd like to fly coach, Push [2]."
    answer = STDIN.gets
    answer.chop!
    break if answer =~ /1|2/
 
    if answer == 1 #User wants FIRST class
    $first = (0..4).find { |i| $available[i] != 1 } # Change display of open seats, first class.
      answer == 1
     $i += 2 #Trying to swap 0 to 1 for 1st class
     $available[$i] += 1
 
end
    if answer == 2 #User wants COACH
     $coach = (5..19).find { |i| $available[i] != 1 } #Seat 6 thru 20 COACH
      answer == 2
      $i += 2 #Trying to swap 0 to 1 for COACH seats.
      $available[$i += 5]
      if nil then
        puts "FULL! Coach"
     if answer.length > 1
       puts "Nothing over 1 digit!"
       redo
    else
      puts "Invalid number, enter 1 or 2."
      Console_Screen.pause
     end
end