2 For loops

I have a problem, my first for loop works and i can see i value going from 0 to 255. However when it comes to the 2nd for loop it is not working. Can someone see why? thank you in advance.

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Sure. Your second for loop starts with j=255, and iterates while j is assigned the value of 0. That is not going to happen very many times.

You probably want j>=0 as the middle clause.