Look into the difference between.
if ((j++) == k)
and
if ((++j) == k)
For the postfix operator the comparison is made BEFORE j is incremented.
(128.22 == 129.22)
For the prefix operator the comparison is made AFTER j is incremented.
(129.22 == 129.22)
[Update]
As Sergey mentioned, it is pretty unusual to use the ++ operator on floating point types. Floating points are a bit complicated and can be tricky to explain.
As we touched on this subject I add two links for further reading:
Look at Solution 5 for this CP question.
The problem with floating numbers[
^]
As a math/programming teacher, you might find this article interesting.
What Every Computer Scientist Should Know About Floating-Point Arithmetic[
^]
Good luck with your teaching.