Question

So I’m aware of the Math.sqrt(number) method in Ruby, but as part of learning the language I thought it’d be a good idea to make some simple functions. I could be going about finding the square root wrong from a fundamental level, but here’s what I did:

def negative?(number)
  number < 0
end

@start = 2

def sqrt(number)
  if negative? number
    puts "Can't do negative"
  else
    if @start**2 < number
      @start += 0.01
      sqrt(number)
    else
      puts "Square root of #{number} is #{@start}!"
    end
  end
end

def start_sqrt
  print "Input text: "
  number = Integer(gets.strip)
  sqrt(number)
end

begin
  start_sqrt
rescue ArgumentError
  puts "Need a positive number!"
end

This works fine for smaller numbers, but when I get to entering larger numbers I need to change the value of @start if I want to get an answer, otherwise it says “stack too deep”. Is there something wrong I’m doing in the code, or is Ruby doing everything fine and I just am asking it to find the square root of a number in a resource-intensive way? I guess this is maybe even less of a programming question and more of a math question, cause I know I could just do:

def sqrt(number)
  if negative? number
    puts "Can't do negative"
  else
    root = number**0.5
    puts "Square root of #{number} is #{root}!"
  end
end

Answer 1

It looks like Ruby is working as expected. You are asking it to find the square root of a number in a resource-intensive way (recursion).

In fact, you have created a stack overflow error. 🙂