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:

Do
  n = RND(20)
  Print n
  Until n = 10
  Print RND(20)
Loop