Subroutines in Perl

Subroutines are like functions in C language.We can define a subroutine by writing sub and then variable name.
For example:
sub read{
$line=<STDIN>;
}
Above is a subroutine which is used to read input from Standard Input Device (such as Keyboard).
When we have to call the subroutine we add & before that subroutine name.
For Example:
           &read;

Program Code:
#!/Perl/bin/perl

print("Enter a sentence\n");

while(1)
{
&read;
last if($line eq "");
print($line);
}
sub read{
$line=<STDIN>;
}
print("done");

Output:

2)Local Variables in Subroutine:

Program Code:
#! /Perl/bin/perl

print("I have declared a local variable and it can't be accessed from outside the subroutine\n");


$calc=&addition;
print("The value returned by subroutine is  $calc \n");
print("The value of local variable outside the subroutine is $total \n Since we are accessing it from outside the subroutine\n");

sub addition
{
my($total)=50;
return $total;
}

Output:

3)Subroutine with Arguments:
A subroutine can have arguments as well.We can accept arguments in subroutine by using the following statement:
my($num1,$num2)=@_;
where num1 and num2 are local variables for this subroutine.@_ is the placeholder.

Program Code:
#! /Perl/bin/perl

print("Enter first number\n");
$first=<STDIN>;

print("Enter second number\n");
$second=<STDIN>;

$calc=&addition($first,$second);
print("The sum of numbers is  $calc \n");

sub addition
{
my($num1,$num2)=@_;
$total=$num1+$num2;
}

Output:

4)Subroutine Forward Reference:
If we will declare the subroutine before calling it then there is no need to & at the time of subroutine calling.

Program Code:
#! /Perl/bin/perl

print("Enter a sentence\n");

sub read;  #forward reference
while(1)
{
#now there is no need to use & before subroutine name but sometimes it doesn't work
&read;
last if($line eq "");
print($line);
}
sub read{
$line=<STDIN>;
}

print("done");

Output: