in reply to how to speed up program dealing with large numbers?

1) What version of perl are you using?

2) As far as I can tell, this isn't really done much in perl:

my $value = 0;
my $range = 0;
my $phiApprox = 0;
my $i = 0;
my $temp = 0;
my $fibValue1 = 0;
my $fibValue2 = 0;

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Declare your variables at (or near) first use, for example:

chomp(my $value = <>);


chomp(my $temp = <>);

my $range = $value + $temp;

my $total;

for (0 .. $range) {
  my $fibValue1 = fib($i);  
  my $fibValue2 = fib($i - 1);
  ...
  ...

  $total++;
}

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Redeclaring variables inside loops is done with alacrity in perl.

3) Note that you can do this in perl:

use strict;
use warnings;
use 5.010;


my $total;
$total++;

say $total;

--output:--
1

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...which would not work in those other languages you know. Yet, paradoxically you will get a warning if you do this:

use strict;
use warnings;
use 5.010;

my $total;

my $result = $total + 1;
say $result;

--output:--
Use of uninitialized value $total in addition (+) at 1perl.pl line 9.
1

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Re^2: how to speed up program dealing with large numbers?
by Solarplight (Sexton) on Mar 22, 2010 at 04:25 UTC

    1) I have v5.8.9 installed, should i be putting that in a use line atop my code

    2) Good to know, yeah thats a C++ habbit. This makes me like perl even more.

    3) Interesting, yeah I wouldn't expect either of those to work. Why does the increment operator work on an uninitialized variable when other math operators don't?

[reply]

      1/ no. Although Perl 5.10 has some nice features that it is worth upgrading to for. say and the new switch processing are nice.

      2/ You ought not be doing that in C++ either! C requires declarations to all be at the start of a block, but in C++ you can put em anywhere.

      3/ The increment and update assignment (+=, *=, .=, ...) treat undef as a special case and "do the right thing". Perl has a fair bit of DWIMery (Do What I Mean) and this is one aspect of that.

      True laziness is hard work
[reply]

        1) Cool, I'll run a portupgade on perl, thanks.

        2) Really, I had been taught that it was at least convention, if not necessary, and I have seen others C++ code that does that.

        3) Interesting, good to know. Thats really cool.

        And again, thanks for all the great info.

[reply]
      1) I would upgrade to perl 5.10+ for say() alone. Having to write "\n" at the end of a print() statement every time will take years off your life. say() is equivalent to print() with a newline at the end of the output.
[reply]
        Except that you spend those years anyway reading programs that alternate between say and print depending on whether they're printing full lines of output at a time.
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