[Za-pm] Passing values

[Nico Coetzee]

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 Hi,

It all depends on how you like to manage you global variables vs local
variables. Perl is very forgiving if you don't use the 'strict' option.
Personally I always include 'use strict' to force myself to pay atentian on
variable scope - something that can stuff you around without the propper
decleration etc.

The other comment I want to make is that it is good practise to use the return
value of you sub's better. Consider the following:

sub double {
   my $num = shift;
   if( $num =~ /\d+/ ) {
      return $num*2;
   }
   return "err";
}

As you can see, we now have error checking build in. By default the sub
returns an error message, unless we have passed a number ( integer ). You
could then call the sub like this:

my $value = 55;
my $returnval = double( $value );
if( $returnval =~ /^err/i ) { print "Error!\n"; }
else { print "Double $value is equal to $returnval\n"; }

On subs that work on global values, I use the return value to indicate if the
value was succesfully updated or not, for example:

sub addone {
   my $num = shift;
   if( ( $num =~ /\d+/ ) && ( $num < 10 ) ) {
      $globalvalue++;
      return 1;
   }
   return 0;
}

Now, consider the following:

if ( addone( $somevalue ) ) {
   # global value was incremented - do want you want here...
} else {
   # global value was NOT incremented - do what you want here...
}

The above example will only increment the global value if the sub recieves a
number smaller then 10.

Also, check out the following little snippet which builds on the previous
example:

#!/usr/bin/perl
my $string = "I am 30 odd years old. Sometimes I whish I was 7 again.";
print "$string\n";
$string =~ s/(\d+)/addone( $1 )/ieg;
print "$string\n";
sub addone {
   my $num = shift;
   if( ( $num =~ /\d+/ ) && ( $num < 10 ) ) {
      $num++;
      return $num;
   }
   return $num;
}

When you run it, you should see something like:

I am 30 odd years old. Sometimes I whish I was 7 again.
I am 30 odd years old. Sometimes I whish I was 8 again.

I think you get the idea.

Cheers

Nico

On Friday 09 January 2004 08:58, Spike wrote:
> Hi All
>
> First query of the year!
>
> If I have a function (sub routine) like :
>
> sub double {
> my $num = shift;
> return $num * 2;
> }
>
> I could say:
>
> $value = 3;
> $value = double($value);
> print "$value
> ";  #   6 expected
>
> My question is how could I write that function so that it works directly on
> the variable that is passed to it in the same way that functions like chomp
> do?
>
> $value = 3;
> double($value);
> print "$value
> ";  #   6 expected
>
>
>
>
>
> Spike Hodge
>
> UNIX Programmer
> M-Web Technology
> 021 596 8496
> 083 294 9593
> Fax 0866721733
>
>
> Click here and make M-Web your homepage
> http://homepage.mweb.co.za

- -- 


BOFH excuse :

_Rosin_ core solder? But...
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