NoMethodError: nil:NilClass 的未定义方法“+”

Question

I tried googling and looking through stackoverflow and still couldnt figure out why does it not work. Essentially, this line of code reads in a file.txt and loop through the line of instructions on the text file

# Load instruction in an array
File.open('file.txt').each do |line|
  line_num += 1
  array.to_a.push line.split(" ")
end

# Loop through the array of Instructions
array.each do |line|
  instruction = line[0]
  value = line[1].to_i

This is the error that I got

NoMethodError: undefined method `+' for nil:NilClass

method block in <main>  in VirtualMemory.rb at line 3
method each in VirtualMemory.rb at line 2
method <main>   in VirtualMemory.rb at line 2

Answer 1

You have to initialize your variables.

line_num += 1

Unless line_num is previously defined this will fail, it's basically the same thing as line_num = nil + 1

This will also fail if you haven't previously defined array , and if you had, then there'd be no point calling to_a .

array.to_a.push line.split(" ")

Answer 2

line_num += 1

is equivalent to

line_num = line_num + 1

Since line_num is not defined, it is nil -- the fix would be to initialize it as 0 before opening the file, or you could do something like:

array = File.open('file.txt').each.map{ |line| line.split(" ")}