When Program Does Not Loop

Unfortunately, Will is right. Not only that, but the condition in line 140 that Z>0 means that when numbers are not swapped, the program does not loop back. The final output is therefore 41563 - not quite what you hoped for! (Unless working in ring of numbers modulo 4, in which case I suppose they are in ascending order; ignore this if you don't have a mathematical background!) This is probably not the best example of the kind of test you are trying to demonstrate.