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## PowerPoint Slideshow about ' Subroutines' - padma

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Subroutines

- sub <subroutine_name> {
- #parameters are placed in @_
- <code>
- .
- .
- return;
- }

Scope

- You can create local variables using my.
- Otherwise all variables are assumed global, i.e. they can be accessed and modified by any part of the code.
- Local variables are only accessible in the scope of the code.

Pass by value and pass by reference

- All variables are passed by value to subroutines. This means the original variable lying outside the subroutine scope does not get changed.
- You can pass arrays by reference using \. This is the same as passing the memory location of the array.

Pass by value

($a,$b) = &sum_prod($x,$y);

sub sum_prod{

my $x=$_[0]; my $y=$_[1];

$s = $x+$y; $p = $x*$y;

return ($s,$p);

}

Pass by value

@a = &sum_prod($x,$y);

#sum in $a[0], product in $a[1]

sub sum_prod{

my $x=$_[0]; my $y=$_[1];

$s = $x+$y; $p = $x*$y;

return ($s,$p);

}

Passing arrays by value

@a=(‘A’,’C’,’G’,’T’);

&print_array(@a);

sub print_array{

my @a = @_;

for($i = 0; $i < @a; $i++) {

print $a[$i]. “ “ ;

}

}

Passing two arrays

@a=(‘A’,’C’,’G’,’T’);

@b=(‘D’,’E’,’F’);

&print_array(@a, @b);

sub print_array{

my @a = @_;

for($i = 0; $i < @a; $i++) {

print $a[$i]. “ “ ;

}

}

Pass by reference

@a=(‘A’,’C’,’G’,’T’);

@b=(‘D’,’E’,’F’);

&print_array(\@a, \@b);

sub print_array{

my $aref = $_[0];

for($i = 0; $i < @$aref; $i++) {

print $$aref[$i]. “ “ ;

}

}

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