The calculated number is indeed 56.99999999999999289457264239899814128875732421875 which is not same to 57 (IEEE 754 binary32 or binary64 can represent this int

The calculated number is indeed 56.99999999999999289457264239899814128875732421875 which is not same to 57 (IEEE 754 binary32 or binary64 can represent this integer exactly). You can verify this with the following: printf("%f\n", 57.0 / 100.0 * 100.0 - 57.0); It just happens that `%f` in C defaults to 6 fractional digits.