Thread Subject: a problem with break syntax

please run this code:

clear;
d=0;
vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
for a=1:10
    while a~=length(vec)+1
        break
    if vec(a)==0 & vec(a+1)~=0
        d=d+1;
        indext(d)=a;
    end
    end
end


the indext vector doses not create in Matlab workspace.
why?

of course I know by chaging the code to :

clear;
d=0;
vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
for a=1:9
        if vec(a)==0 & vec(a+1)~=0
        d=d+1;
        indext(d)=a;
        end
end


the indext vector will create in Matlab workspace.
but i want this vector be create by using while and breake
command.

how sjould i change my source code?by using while.
thanks.

Den Wed, 26 Sep 2007 14:40:59 +0000 skrev ehsan mirrahimi:

> please run this code:
>
> clear;
> d=0;
> vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> for a=1:10
> while a~=length(vec)+1
> break
> if vec(a)==0 & vec(a+1)~=0
> d=d+1;
> indext(d)=a;
> end
> end
> end
>
>
> the indext vector doses not create in Matlab workspace.
> why?
>
> of course I know by chaging the code to :
>
> clear;
> d=0;
> vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> for a=1:9
> if vec(a)==0 & vec(a+1)~=0
> d=d+1;
> indext(d)=a;
> end
> end
>
>
> the indext vector will create in Matlab workspace.
> but i want this vector be create by using while and breake
> command.
>
> how sjould i change my source code?by using while.
> thanks.

Why not remove the for, whiles etc and replace it with

d=find(vec)-1

or am I missing something here?

/PB

PB <pbodin@_REMOVE_THiS_kth.se> wrote in message
<A1wKi.9762$ZA.5842@newsb.telia.net>...
> Den Wed, 26 Sep 2007 14:40:59 +0000 skrev ehsan mirrahimi:
>
> > please run this code:
> >
> > clear;
> > d=0;
> > vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> > for a=1:10
> > while a~=length(vec)+1
> > break
> > if vec(a)==0 & vec(a+1)~=0
> > d=d+1;
> > indext(d)=a;
> > end
> > end
> > end
> >
> >
> > the indext vector doses not create in Matlab workspace.
> > why?
> >
> > of course I know by chaging the code to :
> >
> > clear;
> > d=0;
> > vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> > for a=1:9
> > if vec(a)==0 & vec(a+1)~=0
> > d=d+1;
> > indext(d)=a;
> > end
> > end
> >
> >
> > the indext vector will create in Matlab workspace.
> > but i want this vector be create by using while and breake
> > command.
> >
> > how sjould i change my source code?by using while.
> > thanks.
>
> Why not remove the for, whiles etc and replace it with
>
> d=find(vec)-1
>
> or am I missing something here?
>
> /PB

Prob what PB said. To answer your question let's properly
format your code

> > clear;
> > d=0;
> > vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> > for a=1:10
> > while a~=length(vec)+1
> > break
> > if vec(a)==0 & vec(a+1)~=0
> > d=d+1;
> > indext(d)=a;
> > end
> > end
> > end

So the first time the while statement is satisfied it breaks
out of the loop. Thus your loop SHOULD do nothing as coded.

~Adam

"ehsan mirrahimi" <ehsan.mirrahimi@mathworks.com> wrote in
message <fddr1q$svn$1@fred.mathworks.com>...
> please run this code:
>
> clear;
> d=0;
> vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> for a=1:10
> while a~=length(vec)+1
> break
> if vec(a)==0 & vec(a+1)~=0
> d=d+1;
> indext(d)=a;
> end
> end
> end
>
>
> the indext vector doses not create in Matlab workspace.
> why?

because your code is illogical.

look at this line by line...
> for a=1:10
this is ok, loop for a=1:10
> while a~=length(vec)+1
ok, you will get into the while if a~=length(vec)+1
length(vec)+1 looks like 11 to me, since a=1:10 then you
will always go into the while. so it really doesn't do
anything for you here.
> break
this is the real problem. as soon as you get into the
while loop you break... none of the rest of the code will
be executed between the break and the end of the loop.
what did you think the break was going to do at this
point? There is no use continuing since the code is never
executed.
> if vec(a)==0 & vec(a+1)~=0
> d=d+1;
> indext(d)=a;
> end
> end
> end

this is a good example to learn how to use the debugger
on. you could step through this and immediately see why
you never got to what you wanted to do.

The break statement is performing just fine. In your for
loop, 'a' goes from 1 to 10, so it is never be equal to
length(vec)+1 = 11.
Thus for every 'a' value the while loop will execute and
immediately break, which puts you back in the for loop. So
with that break statement where it is you are basically
doing just this:

clear;
d=0;
vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
for a=1:10
end

exactly as you wrote it!

"ehsan mirrahimi" <ehsan.mirrahimi@mathworks.com> writes:

> please run this code:
>
> clear;
> d=0;
> vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
> for a=1:10
> while a~=length(vec)+1
> break
> if vec(a)==0 & vec(a+1)~=0
> d=d+1;
> indext(d)=a;
> end
> end
> end
>
>
> the indext vector doses not create in Matlab workspace.
> why?

My crystal ball says:

for a=1:10
  if a == 10
    continue;
  end
  if vec(a) == 0 % snip rest of your code
  end
end


-Peter

If you really must use a while and a break, which is not at
all the best way to do this, here is one way. Note this
assumes the output from your second code is the one you want!

clear;
d=1;
vec=zeros(1,10);vec(2)=3;vec(5)=1;vec(8)=4;
while true
    if vec(d)==0 & vec(d+1)~=0
        indext(d) = d;
    end
    d = d+1;
    if d+1 > length(vec)
        break
    end
end
indext = indext(find(indext));