Keep getting undefined method `length' for nil:NilClass (NoMethodError) error

I have written the following code in Ruby that takes input from a user regarding plane and flight details and displays the user inputs as an array in the terminal. For example, if the user enters 3 then the program reads in input 3 times. However, I am getting the following error but I am not sure why: Traceback (most recent call last):
2: from plane.rb:68:in <main>' 1: from plane.rb:65:in main’
plane.rb:56:in print_planes': undefined method length’ for nil:NilClass (NoMethodError)

require ‘./input_functions’
class Plane
attr_accessor :id, :number, :origin, :destination

def initialize (id, number, origin, destination)
    @number = number
    @origin = origin
    @destination = destination


def read_plane()

plane_id = read_integer("Enter plane id:")
plane_number = read_string("Enter flight name:")
plane_origin = read_string("Enter origin airport:")
plane_destination = read_string("Enter destination airport:")
plane =, plane_number, plane_origin, plane_destination) = plane_id
plane.number = plane_number
plane.origin = plane_origin
plane.destination = plane_destination
return plane


def read_planes()
planes_count = read_integer(“How many planes are you entering?”)
while (count<planes_count)


def print_plane(plane)
puts ("Plane id "
puts ("Flight "+plane.number)
puts ("Origin "+plane.origin)
puts ("Destination "+plane.destination)


def print_planes(planes)
index = 0
while (index<planes.length)
puts planes[index]


def main()
planes = read_planes()


Your method read_planes does not return the array of planes. Hence your main method gets nil in planes, and print_planes is receiving nil.

Thank you for your reply, pcl. I have put in the return statement as you suggested. But instead of the program printing out the user input in the terminal I am getting this “#Plane:0x0000557c9678a880”. Why is this happening?

In print_planes, you write puts planes[index] - there is no to_s method in your class Plane, so it uses the default string representation, as you see!

But I think you meant to call print_plane instead of puts …

Hi, pcl
Thank you for replying again. I have tried doing as you suggested by doing the following:
def print_planes(planes)
index = 0
while (index<planes.length)

But I now get an argument error. I am still very new to ruby so I can’t figure out how to fix this.

But I now get an argument error. I am still very new to ruby so I can’t figure out how to fix this.

Take it step by step: What does your print_plane method do? It takes a plane as an argument, and prints its details.

What does your print_planes method do? It takes a list of planes as an argument, looks at each one, and prints its details, by calling print_plane. index is used to refer to each plane in turn, and planes[index] is the current plane.

What are you missing? You have not passed the current plane to print_plane - you were almost there with puts planes[index], instead write:

print_plane planes[index]

You will run into a new problem here: because the @id is an integer, it can’t be printed directly but must be converted into a string. You can add to_s to each line in print_plane, like below:

puts ("Plane id "

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