Array initialization in Perl

Question

How do I initialize an array to 0?

I have tried this.

my @arr = (); 

But it always throws me a warning, "Use of uninitialized value". I do not know the size of the array beforehand. I fill it dynamically. I thought the above piece of code was supposed to initialize it to 0.

How do I do this?

Answer 1

If I understand you, perhaps you don't need an array of zeroes; rather, you need a hash. The hash keys will be the values in the other array and the hash values will be the number of times the value exists in the other array:

use strict; use warnings;  my @other_array = (0,0,0,1,2,2,3,3,3,4); my %tallies; $tallies{$_} ++ for @other_array;  print "$_ => $tallies{$_}\n" for sort {$a <=> $b} keys %tallies;     

Output:

0 => 3 1 => 1 2 => 2 3 => 3 4 => 1 

To answer your specific question more directly, to create an array populated with a bunch of zeroes, you can use the technique in these two examples:

my @zeroes = (0) x 5;            # (0,0,0,0,0)  my @zeroes = (0) x @other_array; # A zero for each item in @other_array.                                  # This works because in scalar context                                  # an array evaluates to its size. 

Answer 2

What do you mean by "initialize an array to zero"? Arrays don't contain "zero" -- they can contain "zero elements", which is the same as "an empty list". Or, you could have an array with one element, where that element is a zero: my @array = (0);

my @array = (); should work just fine -- it allocates a new array called @array, and then assigns it the empty list, (). Note that this is identical to simply saying my @array;, since the initial value of a new array is the empty list anyway.

Are you sure you are getting an error from this line, and not somewhere else in your code? Ensure you have use strict; use warnings; in your module or script, and check the line number of the error you get. (Posting some contextual code here might help, too.)