Learn to Program, 2nd Edition

Local Variables

The following program has two variables:

def double_this num
  num_times_2 = num*2
  puts num.to_s+' doubled is '+num_times_2.to_s
end
double_this 44

44 doubled is 88

The variables are num and num_times_2. They both sit inside the method double_this. These (and all the variables you have seen so far) are local variables. This means they live inside the method, and they cannot leave. If you try, you will get an error:

def double_this num
  num_times_2 = num*2
  puts num.to_s+' doubled is '+num_times_2.to_s
end
double_this 44
puts num_times_2.to_s

44 doubled is 88
example.rb:6:in `<main>': undefined local variable or method `num_times_2' 
      for main:Object (NameError)

Undefined local variable…. In fact, we did define that local variable, ...