Problem Statement

Show a loop which prints random numbers (each number newly generated each loop) from 0 to 19 (inclusive). If a number is 10, stop the loop after printing it, and do not generate any further numbers.
Otherwise, generate and print a second random number before restarting the loop.
If the number 10 is never generated as the first number in a loop, loop forever.

Let's start with the solution:

while (1) {
    my $a = int(rand(20));
    print "$a\n";
    if ($a == 10) {
        last;
    }
    my $b = int(rand(20));
    print "$b\n";
}