#!/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;
}

##</code><code>##

    Ratio Change:  0.1 => 0.101
    Ratio Change:  0.101 => 0.100899100899101
    Ratio Change:  0.100899100899101 => 0.101898101898102
    Ratio Change:  0.101898101898102 => 0.100899100899101
    Ratio Change:  0.100899100899101 => 0.0999000999000999
    Ratio Change:  0.0999000999000999 => 0.0989010989010989
    Ratio Change:  0.0989010989010989 => 0.0988023952095808
    Start percentage ... 10.0000%
      End percentage ...  9.8802%

##</code><code>##

    my $text = "Ratio Change:  $ratio0 => $ratio1\n";

##</code><code>##

    my $text = "Ratio Change:  %7.4f => %7.4f\n", $ratio0, $ratio1;

##</code><code>##

    my $text = sprintf "Ratio Change:  %7.4f => %7.4f\n", $ratio0, $ratio1;

##</code><code>##

    Useless use of private variable in void context at warn.pl line 59.
    Useless use of private variable in void context at warn.pl line 59.

##</code><code>##

    Ratio Change:  %7.4f => %7.4f
    Ratio Change:  %7.4f => %7.4f
    Ratio Change:  %7.4f => %7.4f
    Start percentage ... 10.0000%
      End percentage ...  9.9900%

##</code><code>##

    Ratio Change:   0.1000 =>  0.1010
    Ratio Change:   0.1010 =>  0.1011
    Ratio Change:   0.1011 =>  0.1012
    Ratio Change:   0.1012 =>  0.1013
    Ratio Change:   0.1013 =>  0.1012
    Start percentage ... 10.0000%
      End percentage ... 10.1202%

##</code><code>##

Global symbol "$ratio0" requires explicit package name at ./warn.pl line 26.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 27.
Global symbol "$ratio0" requires explicit package name at ./warn.pl line 27.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 30.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 30.
Global symbol "$ratio0" requires explicit package name at ./warn.pl line 37.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 38.
Global symbol "$ratio0" requires explicit package name at ./warn.pl line 54.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 55.
Global symbol "$ratio0" requires explicit package name at ./warn.pl line 57.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 57.
Global symbol "$ratio0" requires explicit package name at ./warn.pl line 59.
Global symbol "$ratio1" requires explicit package name at ./warn.pl line 59.
Execution of ./warn.pl aborted due to compilation errors.

##</code><code>##

Ratio Change:   0.1000 =>  0.1001
Ratio Change:   0.1001 =>  0.1000
Ratio Change:   0.1000 =>  0.0990
Ratio Change:   0.0990 =>  0.1000
Ratio Change:   0.1000 =>  0.0990
Ratio Change:   0.0990 =>  0.0991
Ratio Change:   0.0991 =>  0.0992
Start percentage ...  0.0992%
  End percentage ...  0.0992%