$arr[$i] = [reverse @{$arr[$i]}];

assigns a new reference (by creating a new anonymous array) to $arr[$i] replacing the reference copied from @_. Without that reference you can't change the contents of @_

Whereas @{$arr[$i]} = reverse @{$arr[$i]} uses the reference copied from @_ to change the existing array elements.

# $#_[$i] doesn't work
sub print2DArray {
  for my $i (0 .. $#_) {  
    for my $j (0 .. $#{$_[$i]}){
      print $_[$i][$j]," ";
    }
    print "\n";
  }
}

[download]
or 
sub print2DArray7 {
  for (@_) {  
    print join " ",@$_;
    print "\n";
  }
}

[download]
poj

In reply to Re^5: Array value changing for some reason by poj
in thread Array value changing for some reason by Silt

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