#!/usr/bin/perl -w
#
#  Demonstrate the importance of "use warnings" and "use strict"!
#  051004 liverpole
#

##############
### Strict ###
##############
use strict;
use warnings;


##################
### Prototypes ###
##################
sub ratio_change($$$$);
sub random_change($);


####################
### Main program ###
####################
my $start_value = my $new_value = 100;
my $start_total = my $new_total = 1000;
my $ratio0 = 100 * $start_value / $start_total;
my $ratio1 = $ratio0;
for (my $i = 0; $i < 100000; $i++) {
    if (ratio_change($start_value, $start_total, $new_value, $new_total)) {
        $ratio1 = $ratio1 = 100 * $new_value / $new_total;
    }
    $start_value = $new_value;
    $start_total = $new_total;
    $new_value = random_change($start_value);
    $new_total = random_change($start_total);
}
printf "Start percentage ... %7.4f%%\n", $ratio0;
printf "  End percentage ... %7.4f%%\n", $ratio1;


###################
### Subroutines ###
###################
sub random_change($) {
    my ($value) = @_;
    (rand(100) > 0.005) and return $value;  # No change 99.995% of the time
    return $value + int(rand(3)) - 1;       # Make a change of -1, 0, or +1
}


sub ratio_change($$$$) {
    my ($value0, $total0, $value1, $total1) = @_;

    my $ratio0 = $value0 / $total0;
    my $ratio1 = $value1 / $total1;

    ($ratio0 == $ratio1) and return 0;      # No change in ratio

    my $text = "Ratio Change:  $ratio0 => $ratio1\n";
    print STDERR $text;
    return 1;
}