Question

echo 65.7 * 100 % 10 // 0

echo 65.6 * 100 % 10 // 9 <---

echo 6560 % 10       // 0

echo 65.5 * 100 % 10 // 0

Can someone please explain why?

EDIT:

for human or non-programmers, the result 9 is apprently wrong.

how can I prevent this "error" when programming?

Answer 1

Because 65.6 in floating point is actually an approximation of 65.6. It is actually marginally less than 65.6, i.e. 65.5999 or similar.

Assuming my wild guess at the actual value is correct, you have 6559.9, which is stripped to 6599 by the modulus operator, then divided by 10 for remainder 9.