The Cycle command ends the current cycle of a For..EndFor, Loop..EndLoop, or While..EndWhile loop, as though the corresponding End were there. It doesn't exit the loop forever; if the loop would have repeated, it goes back to the beginning. However, if the loop is ready to end (if the counter is equal to the end value, for a For loop, or if the condition is false, for a While loop), it exits the loop and continues after the EndFor or EndWhile command.
An example of Cycle in a For loop:
:For num,1,100 : If isPrime(num) : Cycle : Disp num :EndFor
This loop prints all the composite numbers between 1 and 100. Here's how it works: for every number, it first checks whether or not it's prime. If it is, the program goes back to the beginning of the loop with the next number. On the other hand, if the number is composite, the program continues to the Disp num command, then hits EndFor and goes back to the beginning of the loop as well.
If the Cycle instruction is inside multiple loops, one nested in the other, it works with the innermost loop.
560 - Invalid outside Loop..EndLoop, For..EndFor, or While..EndWhile blocks happens when Cycle is used outside a loop.