Why am I getting a different result from std::fmod and std::remainder

Question

In the below example app I calculate the floating point remainder from dividing 953 by 0.1, using std::fmod

What I was expectin

Answer 1

Welcome to floating point math. Here's what happens: One tenth cannot be represented exactly in binary, just as one third cannot be represented exactly in decimal. As a result, the division produces a result slightly below 9530. The floor operation produces the integer 9529 instead of 9530. And then this leaves 0.1 left over.