Re^2: [Homework Question] Subroutines & References

#!/usr/bin/perl
use warnings;
use List::Util qw(sum);

my @list_of_numbers = (1 .. 50);
my $i = ();
my $a = ();

sub mean {
    return sum(@_)/@_;
}

sub above_mean {
    $i == mean(@list_of_numbers);
    foreach (@list_of_numbers) {
        if ($a > $i) {
            print "$a is above mean, which is mean(@list_of_numbers)";
        }
    }
}

print above_mean(@list_of_numbers);
[download]

This now returns:

Use of uninitialized value $a in numeric gt (>) at main.pl line 16.
[download]

However, I thought I declared $a earlier in my program?

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Re^3: [Homework Question] Subroutines & References by choroba (Cardinal) on Feb 11, 2015 at 16:33 UTC
`==` is the numeric comparison operator, not the assignment operator, which is quite similar: `=`. See perlop for details. warnings should have told you: `Useless use of numeric eq (==) in void context at ...` [download] Also, you don't populate `$a` anywhere. Maybe, you meant `foreach my $a (@list_of_numbers) {` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re^4: [Homework Question] Subroutines & References by Hayest (Acolyte) on Feb 11, 2015 at 16:57 UTC
I realized the == error once it executed, however, you helped out with the suggestion of the foreach statement. I've got it running properly now. Thank you!	[reply]
Re^3: [Homework Question] Subroutines & References by AnomalousMonk (Archbishop) on Feb 11, 2015 at 17:21 UTC
`print above_mean(@list_of_numbers);` Just as a matter of curiosity, you might try this variation on the quoted statement: `print above_mean();` Does calling the `above_mean()` function without any parameters make any difference to the value returned by the function? If not, why not? Give a man a fish: `<%-(-(-(-<`	[reply] [d/l] [select]
Re^4: [Homework Question] Subroutines & References by Anonymous Monk on Feb 11, 2015 at 18:57 UTC
calling `above_mean();` function without parameters make does not make any difference to the value returned by the function. I believe this is because @numbers (which I had as the parameter) is already declared inside of my subroutine above_mean - is this accurate?	[reply] [d/l]
Re^5: [Homework Question] Subroutines & References by AnomalousMonk (Archbishop) on Feb 11, 2015 at 19:34 UTC
I would state it slightly differently. The function returns nothing different when it is passed no parameters because it takes no parameters — or more precisely, it does nothing with any parameters it may be passed. The array `@list_of_numbers` is accessed (not declared) within the function. This treats the array as a global variable (even though technically it is lexical). I notice other instances of such access in your functions. Accessing a mutable global (as opposed to a constant) within a function is generally considered a Bad Thing, and is officially Frowned Upon. You have been warned. Give a man a fish: `<%-(-(-(-<`	[reply] [d/l] [select]
Re^6: [Homework Question] Subroutines & References by Hayest (Acolyte) on Feb 11, 2015 at 19:48 UTC
Re^7: [Homework Question] Subroutines & References by AnomalousMonk (Archbishop) on Feb 11, 2015 at 20:38 UTC


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