Ah, sorry, I was confused, the article isn't relevant, indeed.

" As soon as i is smaller than 100 (which it should be after 10 iteration of the loop)"
Not really. i is always smaller than 100, by the conditions you wrote: i starts at 0 and must remain below 100 because of the second part (condition) of the for loop.

Let's analyze your code:
- draw() is called the first time with wCercle at 163.
- The for loop starts with a new i at 0. It will loop 10 times with i incrementing by steps of 10.
- On each of these 10 loops, wCercle diminishes by i.
End of display of the first draw() call.
- draw() is called the second time, with wCercle at -287
- The for loops starts again with a new i at 0, etc.

If you include the declaration of i in the for loop, the i variable inside this loop will be local, not seen from outside, and fresh each time it is run.
You can do a declaration like:
int i; // (at global level, but then use a better, longer name!)
for (i = 0; i < 100; i += 10)
but perhaps a while loop would be better suited.