#!/usr/bin/perl
# read the array from standard input one item at a time
# then sort it , using the built in sort function and the
# bubble sort function I wrote. You will probably never use
# the bubble sort but it is nice to see the code. This was 
# used before the days when the sort command was invented.
#
# usage   perlbubble
#
# You will then be prompted to one at a time enter the array
# elements.
print ("Enter the array to sort, one item at a time.\n");
print ("Enter an empty line to quit.\n");
$count = 1;
$inputline = <STDIN>;
chop ($inputline);
# As long as we do not have an empty line
# read input line into array, increment count of
# array elements, and remove linefeed at end of line before
# entering it into array element
#
while ($inputline ne "") {
        @array[$count-1] = $inputline;
        $count += 1;
        $inputline = <STDIN>;
        chop ($inputline);
}
# now sort the array, the easy way!!
print (" Sort using  built in sort command\n\n");
@array_result = sort (@array);
print ("@array_result \n");
print ("\n\n Now sorting using Bubble Sort \n\n");
# Begin Bubble Sort Section
# Start with first element of array, compare it to the next
# element, if the second element is greater than the first,
# do nothing else, switch them. Now compare the second and
# third element, if the second is less than the third do 
# nothing else switch them. Keep doing this till you get to
# the end of the array. Now you have done the first iteration.
# After the first iteration you can be sure that the last element
# in the array is done. It has bubbled up to the end. So in the
# next iteration you go the array elements - 1. So in the simplest
# case, for 3 elements there would be 2 iterations.
# I have printed inbetween what is happening so you can see
# how it works, as we move through the array one element at
# a time. Note, this is not the most efficient sort. There are at 
# least 8 different kinds. I present this only as a teaching tool.
# I have improved the efficiency by adding in a swapcount. That is 
# if there is no swapping for an iteration we are done!
#
$count = 1;
        print ("This is the original  @array \n");
while ($count < @array) {
        $x = 1;
        $swapcount = 0;
        while ($x < @array) {
                if ($array[$x - 1] gt $array[$x]) {
                        $swapcount++;
                        @array[$x-1,$x] = @array[$x,$x-1];
                }
                $x++;
        }
        if ($swapcount < 1 ) {    
           print ("Finished sorting, leaving now! \n");
           exit;
        }
        print ("After iteration number $count   @array \n");
        $count++;
}
exit;