#!/usr/bin/perl
use strict;
use warnings;

my $kSolarPlanets = 8;

print "How many planets are there? ";

while (defined(my $planets = <>)) {
    chomp $planets;

    if ($planets == $kSolarPlanets) {
        print "Well done there are indeed $kSolarPlanets planets in the solar system";
        last;
    }

    print "Sorry that's not right, try again: ";
}