circumference programV4(working)

#!C:\Strawberry\perl\bin
use warnings;

my $stop = 0;
until ($stop != 0) {


    print "this program will compute the circumfrence of a circle.\n";
    print "\n";
    print "Please enter in the radius of your circle.\n";
    $radius = <STDIN>;
    until ($radius ne "\n") {
        print "please enter a number ";
        $radius = <STDIN>;
    }

    print "The radius of your circle is ";
    print 2 * 3.141592654 * $radius;
    print "\n";
    print "do you want to calculate another?(yes/no)\n";
    $stop = 0;
    $answer = <STDIN>;
    if ($answer eq "no\n") {
        print "exiting.... \n";
        $stop = 1;

    } else {
        $stop = 0;
    }
}