#!/usr/bin/env perl

# unless == if not
#

my $target=10;

my $while_count=0;
while ($while_count < $target){
  $while_count++;
}
print "while_count = $while_count\n";

my $unless=0;
unless ($unless >= $target){
 $unless++;
}
print "unless = $unless\n";

my $until_count=0;
until ($until_count >= $target){
 $until_count++;
}

print "until_count = $until_count\n";

#######

#!/usr/bin/env perl
sub regular_way {
 my $n = shift;
 my $sum;
 foreach (1 .. $n){
  $sum += $_;
 }
 $sum;
}

sub recursive_way {
 my $current=shift;

 if ($current == 0) {
  return 0;
 }
 else {
  return ($current + recursive_way($current - 1));
 }
}

#main start
my $r = regular_way 100;
print "1+...+100=", $r, "\n";

$r = recursive_way 10;
print "1+...+10=", $r, "\n";

#######

#!/usr/bin/env perl

#modify a scalar inside a subroutine
sub try_add {
 my $val = shift;
 $val++;
}

my $n=0;
try_add $n;
print "n = $n\n";

sub add_one {
 my $ref = shift;
 $$ref++;
}

add_one \$n;
print "n = $n\n";


####
#!/usr/bin/perl

my $x  = 10;
my $rx = \$x;           # reference to $x

$$rx = $$rx * 2;        # change $x via $xr, same as $x = $x * 2;

print $x;       #20
print $$rx;     #20
print $rx ;     #SCALAR(0x8270a97b0)

print "\n";

my @a = (1..3);         # init array and assign vals
my $ra = \@a;           # ra reference to array

my $i = 0;

foreach (@$ra){
    print("$ra->[$i++] \n"); # $a[0]
}

my %h = (1, 'january', 2, 'february', 3, 'march'); #hash 1 => 'january' ...
my $rh=\%h;

foreach (keys %$rh){
 print "$_ $$rh{$_}\n"; # $h{1}
}

###
#!/usr/bin/env perl

my @names = qw /Yabba Dabba do/;

my $names_ref  = \@names;

print "$names_ref\n";           # ARRAY(0x703dcf2)

print "@$names_ref\n";          # Yabba Dabba do
print "@{ $names_ref }\n";      # same as above, but clear. it use {} to
print "@names\n";               # original way

print "number of names = "   , scalar @names, "\n";
print "max index of names = ", $#names      , "\n";

#
#                    Array                Array Reference
#Whole array:        @names               @{ $names_ref }       # same as @$names_ref
#Element of array:   $names[0]            ${ $names_ref }[0]    # saem as $$names_ref[0]
                                          $names_ref->[0]       # different a=>

#Size of array:      scalar @names        scalar @$names_ref
#Largest index:      $#names              $#$names_ref

#######
#!/usr/bin/env perl

my @array = (100..103); # use list to init array
my $refa = \@array; # reference to array
print  $$refa[0], "\n";
print $refa->[0], "\n";

my %h = ( john => 194, jack => 168 );
print "jack height is ", $h{jack}, "\n";

%h=(); # init hash, make it empty
%h= ( john => [174,67], jack => [168, 72] ); # anonymous array as value
print "jack height and weight are ", $h{jack}[0], " ", $h{jack}[1], "\n";

my @heart_rate=(174, 155, 181, 160);
my $refa=\@heart_rate;
%h=();
#%h= ( john => @heart_rate); # wrong, since hash treat this array as value
%h= ( john => $refa );

print "john heart beating: ";
foreach ( @$refa ) {
 print "$_ ";
}