Will result always be the floor of the division? What is the defined behavior?
Not quite. It rounds toward 0, rather than flooring.
6.5.5 Multiplicative operators
6 When integers are divided, the result of the / operator is the algebraic quotient with any
fractional part discarded.88) If the quotient a/b is representable, the expression
(a/b)*b + a%b shall equal a.
and the corresponding footnote:
- This is often called ‘‘truncation toward zero’’.
Of course two points to note are:
3 The usual arithmetic conversions are performed on the operands.
5 The result of the / operator is the
quotient from the division of the
first operand by the second; the
result of the % operator is the
remainder. In both operations, if the
value of the second operand is zero,
the behavior is undefined.
[Note: Emphasis mine]