use warnings;
use strict;
use Scalar::Util 'looks_like_number';
my $i;
$i=0;
while ($i==0)
{
        print "Welcome to an interactive Perl program. Enter either q or Q to terminate the program or c to continue. Enter your key now: ";
        my $input;
        $input = <STDIN>;
        if (($input ne "q") || ($input ne "Q") || ($input ne "c"))
        {
                print "Welcome to an interactive Perl program. Enter either q or Q to terminate the program or c to continue. Enter your key now: ";
        }
        elsif (($input eq "q") || ($input eq "Q"))
        {
                exit;
        }
        else
        {
                print "Please enter one x coordinate: ";
                my $x1;
                $x1 = <STDIN>;
                print "Please enter one y coordinate: ";
                my $y1;
                $y1 = <STDIN>;
                print "Please enter one z coordinate: ";
                my $z1;
                $z1 = <STDIN>;
                print "Please enter a second x coordinate: ";
                my $x2;
                $x2 = <STDIN>;
                print "Please enter a second y coordinate: ";
                my $y2;
                $y2 = <STDIN>;
                print "Please enter a second z coordinate: ";
                my $z2;
                $z2 = <STDIN>;
                my $answer;
                if (($x1 !~ /^-?0/ && looks_like_number($x1)) && ($y1 !~ /^-?0/ && looks_like_number($y1)) && ($z1 !~ /^-?0/ && looks_like_number($z1)) && ($x2 !~ /^-?0/ && looks_like_number($x2)) && ($y2 !~ /^-?0/ && looks_like_number($y2)) && ($z2 !~ /^-?0/ && looks_like_number($z2)))
                {
                        $answer = sqrt(((($x2)-($x1))**2)+((($y2)-($y1))**2)+((($z2)-($z1))**2));
                        print "The distance between the two points is $answer";
                }
                else
                {
                        print "Error, you must only input numbers.";
                }
        }
}