In Perl arrays, the index '-1' accesses the last element in the array. '-2' accesses the second-to-last. ...and so on, down to '- scalar @array', which will be the same element as '$array[0]'.

This makes it easy to simultaneously count upward and downward; just do a numeric negation of sign, and adjust for off-by-one.

@numbers = ( 100, 200, 300, 400, 500 );

$reversed[$_-1] = $numbers[-$_] for 1 .. @numbers;

print "$_\n" for @reversed;
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Here's just about the only useful use of $[ (which should be avoided, even here).

@numbers = ( 100, 200, 300, 400, 500 );

{
  no warnings 'deprecated';
  local $[ = 1;             # Don't do this... example only.

  $reversed[$_] = $numbers[-$_] for 1 .. @numbers;
}

print "$_\n" for @reversed;
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The array index negate-adjust trick (easily encapsulated in a subroutine) is particularly useful when dealing with 'large' arrays, the reversed elements of which can then be accessed in-place: no reversed copy, possibly quite expensive in terms of space, need be made.

I want to do it without using any predefine function

I.e., "This is homework".

try the push function to add an element to an array.