# FAQ: Loops & Iterators - Looping with 'While'

This community-built FAQ covers the “Looping with ‘While’” exercise from the lesson “Loops & Iterators”.

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## FAQs on the exercise Looping with ‘While’

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Hi. This is from Lesson 5: Loops & Iterators Section 14 Looping with “while”.

This is the code that was given:
i = 3
while i > 0 do
print i
i -= 1
end

1. In the above example, we create a variable called `i` and set it to `3` .

2. Then, we print out `321` since we execute the loop as long as `i` is positive.

I would greatly appreciate if someone could explain this to me as I don’t understand where the 321 comes into play.

Thank you very much!

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The 2 lines of code between `while` and `end` will be repeated until the condition specified in the `while` statement is no longer true. `print i` prints the value of `i` and then `i -= 1` subtracts 1 from the value of `i`, so the first iteration of the `while` loop prints 3 (the initial value of i), the second iteration prints 2 ( `i -= 1` changed i to 2), etc. Since we’re using `print` without adding any spaces or new lines, the output is `321` Hope this helps!

2 Likes

Thank you very, very much for your easy to understand explanation.
Now, I can finally go to bed!

1 Like

I thought { and } could replace do and end respectively. Is this not the case? why do I get this?

1 Like

Hello, @cloudrockstar46685. Welcome to the forum!
You can’t use curly braces `{ }` with a while loop in Ruby.
You can omit the `do`:

``````n = 1
while n <= 50
print n
n += 1
end
``````

You may find this topic interesting: https://stackoverflow.com/questions/35726738/how-to-do-a-one-liner-while-loop-in-ruby-using-curly-braces
Happy coding!

3 Likes

Why doesn’t running this code cause the checklist to verify that I’ve completed the assignment? Is it because the code is going down from 50 instead of up from 1? Also, why does changing “i = 50” to “i <= 50” fix the problem by reversing the order?

Hello, @data8822600657.

Welcome to the forums.

The exercise specifically asks us to count up, so yes, that is why you don’t receive the check mark for passing.

Not sure I follow you here. Changing only the first line of your code from `i = 50` to `i <= 50`, and leaving your remaining code as is should throw an error. `i <= 50` is a comparison not an assignment, so you will get an `undefined` error. To count up rather than down you would need to assign `i` a value of `0` initially, and then in your `while` statement you would use `i <= 50`, and inside the body of the `while` loop you would increase `i` by `1` each time rather than decrease.

1 Like

I have apparently completed the task satisfactorily, but I’m getting a lot of warning messages in between the print results.

U need to space between your OneToFifty and =, It should looks like this

OneToFifty = 1
while OneToFifty < 51
print OneToFifty
OneToFifty += 1
end

Under “Loops and Iterators. Looping with while”, this works:

``````i = 0
while i <= 50 do
print i
i+= 1
end
``````

however, this doesn’t:

``````i = 0
while i <= 50 {
print i
i+= 1
}

``````

Why not? A bit earlier in the chapter it is stated that curly brackets and do/end are interchangeable. Yet the code only works when using the do/end keywords.

This is the error I get:

``````(ruby):1: syntax error, unexpected '{', expecting keyword_do_cond or ';' or '\n'
(ruby):4: syntax error, unexpected '}', expecting end-of-input
``````

Not sure if block syntax works when there are line breaks.

``````arr.each { x | puts x }
``````

For multiple lines we need to use `do` and `end` (or some other construct) as I understand it.

When the lesson first introduced While Loops it didn’t use ‘do’ in the code. But in this exercise it has. Is there a reason? It seems to work without ‘do’.

old code without do:

``````i = 3
while i > 0
print i
i -= 1
end
``````

new code with do:

``````i = 3
while i > 0 do
print i
i -= 1
end
``````

Both give the same result.

The second example is exactly the same as the first, given that `do` is optional in that syntax, meaning it is implied when absent. `do`, itself is the opening of a code block.

Note that if the code is written as,

``````i = 3
do
print i
i -= 1
while i > 0
``````

it is not the same loop since this one will run at least once. Pretty sure I read once, a long time ago, that this code is not recommended, as in discouraged for the simple reason that it is not the same as the opening examples, which can lead to confusion on the part of the reader. If the syntax is still supported, one may wish to do some further research on the point.

2 Likes