my %hash= initvalues();

...

%hash= initvalues();

...

sub initvalues {
  return ('a'=>0, ...);
}

##</code><code>##

my %hash;
inithash(\%hash);

....

inithash(\%hash);

...

sub inithash {

my $h= shift;
$_[0]= { 'a'=>0, ... }; #note the curled braces #CORRECTED
%$h= ( 'a'=>0, ... ); #alternative to the previous line
}