Hi John,
On Monday 03 May 2010 17:42:16 John W. Krahn wrote:
> Samuel Williams wrote:
> > Dear Friends,
>
> Hello,
>
> > It would also be great if someone could rewrite the Perl source code
> >
> > example so that it is as close as possible to the C implementation:
> > http://programming.dojo.net.nz/languages/c/index
> >
> > /* Include the standard input / output functions */
> > #include <stdio.h>
> >
> > int main()
> > {
> >
> > /* Initialize the array of doors to 0 (closed) */
> > char is_open[100] = {0};
>
> Why are you creating an array of 101 elements when you only use 100?
> Your comment says you initialize the array but you only initialize the
> first element.
Actually, in C:
1. A << type_t myarray[100]; >> will initialise an array that can be indexed
from 0 to 99 - 100 elements in total. Likewish myarray[10] will be indexed
from 0 to 9, etc.
2. The {0} is a shortened initialisation to allocate all the elements as 0.
>
> > int pass, door;
> >
> > /* Process the doors */
> > for (pass = 0; pass < 100; ++pass)
> >
> > for (door = pass; door < 100; door += pass+1)
> >
> > is_open[door] = !is_open[door];
> >
> > /* Print out the results */
> > for (door = 0; door < 100; ++door)
> >
> > printf("Door #%d is %s.\n", door+1, (is_open[door] ? "open." :
> > "closed."));
> >
> > return 0;
> >
> > }
>
> sub main()
> {
1. Why did you put everything in a main fuction? Perl is not C.
2. Why the "()" after the main? You shouldn't specify prototypes.
> # Initialize the array of doors to 0 (closed)
> $is_open[100] = 0;
1. Why didn't you declare @is_open? You should have used strict and warnings.
2. This will initialise the element of index 100 (actually the 101st element)
to 0 and all the elements before it (assuming they did not exist beforehand)
to undef. You probably want << @is_open = ((0) x 100) >> instead.
>
> # Process the doors
> for ($pass = 0; $pass < 100; ++$pass){
1. PBP recommends against doing C-style for loops.
2. you should declare pass again.
3. You should have some space before the "{" (I start it on a newline and have
my reasons for that but I accept the other style).
> for ($door = $pass; $door < 100; $door += $pass+1){
> $is_open[$door] = !$is_open[$door];}}
Ahmmm.. why didn't you put the two "}" in separate lines? Perl is not Lisp.
>
> # Print out the results
> for ($door = 0; $door < 100; ++$door){
> printf("Door #%d is %s.\n", $door+1, ($is_open[$door] ? "open."
>
> : "closed."));}
Just a note - the C program has a bug where the strings had a trailing "."
which was also included in the printf's formatting string. It should not be
reproduced in the Perl program.
Regards,
Shlomi Fish
>
> return 0;
> }
>
>
>
>
> John
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