Re: Simple (and probably stupid) question about for loops

[Maynard Wright]

On Tuesday 25 May 2010 07:42, John W. Eaton wrote:
> On 25-May-2010, AlbFrigerio wrote:
> | Hi everyone, I believe I'm really rusty in using Octave cause I'm trying
> | to do a very simple thing (in my mind) but I cannot succed in it. I tried
> | to read the guide and some posts on for loops, but I haven't managed
> | anything.
> |
> | Here it is my question : is it possible to update the value of the for
> | index inside the loop?
> |
> | For example, I wrote the following code :
> |
> | for k=1:10
> |   k
> |   if k==2
> |      k=5;
> |   endif
> | endfor
> |
> | I'd like the output to be : 1 2 6 7 8 9 10 , but it always gives me 1 2 3
> | 4 ... 10 . It sounds like the k variable in the loop to be completely
> | different from the one used in the loop.
>
> It's not a different variable.  The value is reset each time at the
> top of the loop.
>
> jwe

Octave's behavior here differs from C.  If you write the comparable code in C 
it is possible to modify k within the loop and to produce the output that 
lacks the integers 3, 4, and 5.  This results from the definition of for() in 
terms of while() by K&R.  I haven't checked to see whether any subsequent 
developments in C or C++ have changed this, but my compilers support the K&R 
behavior.

Note that this doesn't mean that Octave is wrong, just different from another 
language, something we need to keep in mind if we work in both.

Maynard Wright