#!/usr/bin/perl -w
use strict;
use Regexp::Common;

my $a = prompt("A? = ");
my $b = prompt("B? = ");
my $c = prompt("C? = ");

my $root = sqrt(($b**2) - 4 * $a * $c) / (2 * $a);
my $ans1 = -$b + $root;
my $ans2 = -$b - $root;

print "Answers: $ans1 AND $ans2\n\n";

sub prompt {
    my $var;
    do {
        print $_[0];
        $var = <STDIN>;
        chomp $var;
    } while ($var !~ /\A$RE{num}{real}\z/);
    return $var;
}