my $a = 10;

print "$a ";
change($a);
print "$a";

sub change {
    $_[0]++;
}

##</code><code>##

my $a = 10;

print "$a ";
change($a);
print "$a";

sub change {
    my $param = shift;
    $param++;
}

##</code><code>##

# contrived example: there usually isn't a good reason
# to have references to scalars.
my $a = 10;
my $b = \$a;

print "$$b ";
change($b);
print "$$b";

sub change {
    my $param = shift;
    ${$param}++;
}

##</code><code>##

my $a = 10;
my $b = \$a;
my $c = 4;
print "$$b ";
change($b);
print "$$b";

sub change {
    $_[0] = \$c;
}