Change variable increment/decrement into mid-loop?

Hello.
There is a some loop, which monitors keypress, updates display, etc.
Also in loop is variable, which should increase from 1 to 100 and then decrease from 100 to 1.
Is there any way to do it in simple way? without splitting loop into two parts?

Something like this perhaps?

Code:

---

Cnt VAR BYTE
Dir VAR BIT

UP CON 1
DOWN CON 0

SomeLoop:
  ' Monitor keypress
  ' Update Display
  ' etc

  IF Dir = UP THEN
    Cnt = Cnt + 1
  ELSE
    Cnt = Cnt - 1
  ENDIF

  IF (Cnt = 100) OR (Cnt = 0) THEN
    Dir = ~Dir    ' Invert direction
  ENDIF

  Goto SomeLoop

---

Yes, thanks!
On spectrum, I was doing this by changing the sign of increment variable, but since in PBP we have no negative numbers....

And yes, CNT=1 should be added in the beginning, or absolutely unexpected behavior will be generated (just tested) :D

Regarding negative numbers, as long as both variables are of the same size what you did will work:

Code:

---

Cnt VAR BYTE
Add VAR BYTE

Cnt = 100
Add = -1

Cnt = Cnt + Add  ' Cnt now = 99

---

But if Cnt was a WORD and Add a BYTE then Cnt woul equal 354.