use strict;
use warnings;


sub add{
	
	my ($x, $y) = @_;
	my $sum = $x + $y;
	print "Sum within function: $sum\n";	
	return ($sum);
}

my $bb=\&add(10,1); 
print $bb."\n"; 

my $cc=\&add; 

print $cc."\n"; 


##</code><code>##

Sum within function: 11
SCALAR(0x3f7e24)
CODE(0xa3e58c)


##</code><code>##

use strict;
use warnings;

our $static_counter = 1;

sub add{
	
	my ($x, $y) = @_;
	my $sum = $x + $y;
	print "Sum within function: $sum\n";	
	return ($sum);
}

sub counter {
	my $cnt = $static_counter++;
	print "Value of count in subroutine  $cnt\n";
	return($cnt);
}

sub mm{
	my ($x, $y, $add_ref, $counter_ref) = @_;
	
	my $cnt_in;
	my $add_in;
	my $mul = 1;
	

	
	$mul = ($x * $y * &$add_ref(10,1) * &$counter_ref());
	print "Multi : $mul\n";	
	
	$add_in = $add_ref->(20,5);  ### Getting Error Here 
	###  Not a Code Reference
	$mul = ($x * $y * $add_in * $counter_ref->()); 
	print "Multi : $mul\n";	 	
	
	return $mul;
	
}

sub aa {	
	my $z; 
	$z =  mm(4,5, \&add, \&counter);
	$z =  mm(4,5, \&add, \&counter);
}


aa();




##</code><code>##

Sum within function: 11
Value of count in subroutine  1
Multi : 220
Sum within function: 25
Value of count in subroutine  2
Multi : 1000
Sum within function: 11
Value of count in subroutine  3
Multi : 660
Sum within function: 25
Value of count in subroutine  4
Multi : 2000