I'm a beginner to perl also. This was a good problem for me to try. Here's my code. I left my debugging print statements in there. From what I observed, the G = 2 and the I = G blocks will never execute. G is set to 0 in the H = 2 block and never change to anything else. I and G never equal the same thing until the last else statement and the program doesn't loop back around that I = G statement again.

use strict;
use warnings;

my $G = 18;
my $H = 2;
my $I = 13;

print "Initial values\n";
print "g=$G\th=$H\ti=$I\n";


if($H == 2)
{
    &ChangeGI($G, $I);
}
print "Values After H ==2\n";
print "g=$G\th=$H\ti=$I\n";


while ($I > 7)
{
    &ChangeHI($H, $I);
    print "In while loop I > 7\n";
    print "h=$H and i= $I";
}
print "After while loop\n";
print "g=$G\th=$H\ti=$I\n";


if($G == 2)
{
    &ChangeG($G, $H);
}
print "After G ==2\n";
print "g=$G\th=$H\ti=$I\n";

if($I == $G)
{
    &ChangeG($G, $H);
}
else
{    
    &ChangeHI($H, $I);
}
print "After IF  I== G\n";
print "g=$G\th=$H\ti=$I\n";

print "The final results are G\: $G   and H\:  $H   and  I\: $I\n";

#######################
sub ChangeGI
{
    while($I > 5)
    {    
        $I = $I - 3;
        $G = 0;
    }
}

sub ChangeHI
{
    $H = $H + 2;
    $I = $I - 4;
}

sub ChangeG
{
    my ($G, $H) = @_;
    $G = $G + 1;
    $H = $H -1;
}


#Initial values
#g=18    h=2     i=13
#Values After H ==2
#g=0     h=2     i=4
#After while loop
#g=0     h=2     i=4
#After G ==2
#g=0     h=2     i=4
#After IF  I== G
#g=0     h=4     i=0
#The final results are G: 0   and H:  4   and  I: 0
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