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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.javascript
Subject: Re: Logic problem, i always had problem translate until statements into while
Date: Fri, 27 Jan 2017 11:02:43 +0000
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jonas.thornvall@gmail.com writes:

> Den fredag 27 januari 2017 kl. 00:06:24 UTC+1 skrev Ben Bacarisse:
>> jonas.thornvall@gmail.com writes:
>> 
>> > Den torsdag 26 januari 2017 kl. 22:24:32 UTC+1 skrev jonas.t...@gmail.com:
>> >> Den torsdag 26 januari 2017 kl. 21:29:05 UTC+1 skrev Ben Bacarisse:
>> >> > jonas.thornvall@gmail.com writes:
>> >> > 
>> >> > > do until (regular == true && connected == false )
>> >> > >
>> >> > > I honestly feel a bit lost, because i think they are so easy to code
>> >> > > using do until.
>> >> > 
>> >> > What as the initial values of 'regular' and 'connected'?
>> >> > 
>> >> > > So how should i think about it?
>> >> > 
>> >> > Provided the initial value of the resulting while condition is true you
>> >> > just need to invert it:
>> >> > 
>> >> >   while (!(regular == true && connected == false)) ...
>> >> > 
>> >> > You can use De Morgan's laws to simplify that if you like:
>> >> > 
>> >> >   !(A && B) <=> !A || !B
>> >> >   !(A || B) <=> !A && !B
>> >> > 
>> >> > in your case
>> >> > 
>> >> >      !(regular == true && connected == false)
>> >> >   => !(regular == true) || !(connected == false) 
>> >> >   => regular != true || connected != false
>> >> > 
>> >> > which I'd just write as
>> >> > 
>> >> >   while (!regular || connected) ...
>> >> > 
>> >> > Often, the use of do ... until is simply an error (while is needed more
>> >> > often in algorithms than do...until).  In those cases there is no need
>> >> > for the loop to execute at least once and you don't need to check that
>> >> > '!regular || connected' is initially true.
>> >> > 
>> >> > -- 
>> >> > Ben.
>> >> 
>> >> Unfortunately they are both false,
>> 
>> Why is that unfortunate?  If they are both initially false your
>> do...until can be written as a while with the condition negated.
>> 
>> <snip>
>> -- 
>> Ben.
>
> I feel you dodged the obstacle,

Probably.

> i asked if the boolean is
> generated/searched and found within loop and all values of the truth
> table can be found, how do you set the start condition, can i set the
> boolean to "null" at start?

If you asked this I missed it, but I couldn't answer it anyway because I
don't know what it means.

-- 
Ben.