How to Reverse an Array

Virtually all programming languages use an array structure to store a list of data. For example, "array(76, 3, 5)." The reversed array would contain the same data but backwards i.e. "new_array(5, 3, 76)." Perl, a freely accessible programming language, allows you to implement a very elegant algorithm to reverse an array that requires only four lines of the code. The algorithm uses Perl built-in functions "pop" and "push."

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Computer

The Steps

1. Obtain array data from the main program. Another array "new_array" will contain reversed data.

2. Remove the last element from the initial array using the "pop" function.

3. Add that element as the first one to the new array with "shift" function.

4. Repeat Steps 2 and 3 until the initial array becomes empty; all its elements get transferred to the new one in reverse order.

5. The working Perl program is below
   #Program starts
   my $array=[qw(1 2 6 7.4 25 9 12.6 2 6)]; #Example array
   my $new_array=[];
   print "@$array \n";
   reverse_array($array, $new_array);
   print "@$new_array \n"; #Printing the new array
   exit;
   
   sub reverse_array {
   my($array, $new_array)=@_; #Step 1. Read initial array
   while(@$array) {
   my $entry=pop (@$array); #Step 2. remove the last element of the initial array
   push @$new_array,$entry; #Step 3. Add that element to the new array as the first
   }
   }

6. The program output is as follows
   1 2 6 7.4 25 9 12.6 2 6 <---initial array
   6 2 12.6 9 25 7.4 6 2 1 <---new array
   The array is reversed.

References

• "Programming Perl", L. Wall, 2000.

Resources

• Perl Functions