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Ruby

Posted by Anthony Ross
Anthony Ross
2,756 Points

Understanding the "Until" loop

I'm working with the following bit of Ruby code: 

name = ""

until name == "Jason" do 
    name = gets.chomp
    puts "Your name is: #{name}"
end

I understand that this loop will keep going until it's given "Jason". What I don't understand is why when I type "Jason", I still see the puts "Your name is: Jason" and then the program ends.

I'm wondering why the 'puts' method was used here, when one would think the loop wouldn't even run now that it's been given the value of "Jason" (so the next 2 lines wouldn't be used).

What am I not understanding?

3 Answers

James Barnett
James Barnett
39,199 Points
James Barnett
James Barnett
39,199 Points

Maybe this flowchart will help

James Barnett
James Barnett
39,199 Points
  1. name is initalized to null
  2. check if name is set to "Jason"
  3. Since name is set to null continue into the until block
    1. Type "James" at the prompt
    2. parse "James" from input
    3. set name equal to James
    4. print the contents of name which is currently "James"
  4. check if name is set to "Jason"
  5. since name was set to "James" in step 3-3 continue into the until block
    1. Type "Jason" at the prompt
    2. parse "Jason" from input
    3. set name equal to Jason
    4. print the contents of name which is currently "Jason"
  6. check if name is set to "Jason"
  7. Since name is set to Jason in step 5-3 don't execute the until block
Anthony Ross
Anthony Ross
2,756 Points

Oh, my duh! YES! Sigh, thank you sir - that makes total sense!

Andre' Jones
Andre' Jones
26,671 Points
Andre' Jones
Andre' Jones
26,671 Points

the loop is will always cycle through at least once as long as ur name is set to an empty string as you have done or something other than Jason. when ur trying to understand loops or any other methods just take some example inputs and go down the line and see what u get.

Anthony Ross
Anthony Ross
2,756 Points
Anthony Ross
Anthony Ross
2,756 Points

Hi James - That flowchart seems to prove my point. if name == Jason it jumps to "End". It doesn't get to "read name" or to "print name", so if I enter Jason the program should just end, not "Your name is Jason".

Andre' I'm not sure I understand what you're outlining.