Question about Loops.

tytadas · November 2016

I do realize this question might not be the best here, but I need to understand loops better. So I'll try to risk and ask the question.

I know loops and I do pretty much understand what they are made for and what do they do. But I'm a bit Lost.

While loop syntax is:

while(condition)
do
statement
end

For loop conditions is pretty much the same, but it has init, max/min value, increment, everything else is the same.
But repeat..until loop is a bit different.

repeat
statement
while

My point here is, that I can't get out by myself the information.
Why does 2 loops has the "do" line and repeat..until loop does not?
What's the function or should I say purpose of the "do" line in the loop? What does it stand for? What does "do" line represents?

Thank you.

antix · November 2016

Here's an example...

local counter = 0
 
while counter ~= 100 do -- Loop 100 times
  counter = counter + 1
end
 
print(counter) -- will print "100"
 
counter = 0
repeat
  counter = counter + 1
until counter == 200 -- repeat the loop until this condition is met
 
print(counter)

Does that make it easier to grasp?

tytadas · November 2016

@antix Yes, I do understand it. But my point of the question was about "do" line. Maybe it's not that important to know everything about the syntax of all the loops.
Thank you for answering

n1cke · November 2016

> Why does 2 loops has the "do" line and repeat..until loop does not?
'do' is just a keyword to separate condition from statements in loops. Without this separator it will be harder to read them, especially when condition and statements are on the same line.
'while - do - end' loop checks it's condition first and if it is equal to false or nil then statements will be skipped even at first loop iteration. But there are few situations when you need to execute loop statements at least once, no matter of condition. Of course you can copy-paste statements to a place above your loop but such code will be harder to maintain: if you will change statements in your loop then you will need to copy-paste them again. That's why 'repeat - until' loop is useful here: it first executes it's statements and only then checks a condition. And 'repeat-until' doesn't use 'do' keyword because it's easier to differentiate it from 'while-do' loop.

tytadas · November 2016

Hoora! I was expenting to get the answer from you! Thanks:))

SinisterSoft · November 2016

'do' will end the condition in the tokeniser. It's there so that you can write:

n=100
while n=0 do n=n+1 end

just like you could write:

n=100
repeat n=n-1 until n=0

(don't forget though that repeat will execute the loop at least once even if the condition isn't met, but the while may not if the condition isn't met straight away)

totebo · November 2016

I also understand and use both while and repeat, and I have also felt it is an inconsistent syntax. I really want an end in there in the repeat loop, but if course that would lead to more confusion.

tytadas · November 2016

Yeaa I do believe that you can't survive without using loops while coding or can you?

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