Re: How am i doing?

[cavac]

Overall, a good start. The main some problems that i see:

• You are developing for an ancient version of Perl. Since then, subs (=functions) can now be declared to directly take function arguments.
• You are using recursion. Unless you really know what you are doing (and set strict recursion limits), that's something that can backfire quite easily. (And this isn't a problem that requires recursion).
• You are using global variables when you don't have to. That makes code re-use much harder.

Here is a version i quickly "modernized" and "cavacized". I'm note sure if the result is correct, though, since i don't have the description in the book available (and i had only a few minutes during my afternoon break to write this).

#!/usr/bin/perl

# Latest perl version with the newest features and bugfixes
use v5.40;

# Do all kinds of automatic checking of the program code
use strict;
use warnings;

# Great debugging tool to quickly print a complex structure (array, ha
+sh, scalar, whatever) to the console
use Data::Dumper;

# Call the calculation main routine
my $max = 100; # 4_000_000;
my @baseframe = (1, 2, 3);
my $result = fib($max, \@baseframe); # Call with a REFERENCE to @basef
+rame, so subs can modify it

# Print the final result
print 'Final: ', $result, "\n";

# For debugging, print the final state of @baseframe
print 'Final @baseframe: ', Dumper(\@baseframe), "\n";

# And end scene...
exit(0);


# This does ONE round of the calculation, no deep recursion
sub fib_one_round($frame) {
    $frame->[0] = $frame->[0] + $frame->[1];
    $frame->[1] = $frame->[2];
    $frame->[3] = $frame->[2];

    if(($frame->[0] %2) != 0) {
        return $frame->[0];
    }

    return 0;
}

# This does the main loop. We are working on an array *reference*, so 
+fib_one_round can modify the array
sub fib($max, $frame = [1, 2, 3]) {
    my $result = 0;

    # Loop until the max value has been reached
    while($result < $max) {
        $result += fib_one_round($frame);

        # Print the intermediate results for debugging
        print $result, "\n";
    }

    return $result;
}

Basically, i replaced the recursion with a while loop, added modern sub-signatures, made sure the "frame" we are working on is passed through the function calls (instead of global vars). And removed/inlined the count() function because it's a single if-statement that doesn't warrant the performance overhead of a funtion call. And, oh, added an example of Data::Dumper to show how you can easily look at complex data structures for debugging.

I also moved the main code above the subs, because that makes it easier if you come back at a later time to the code. The high level stuff is at the beginning (showing/explaining what the script does), the nitty-gritty details that you might never have to touch again are below that.

Hope that helps.