Integers form Subring of Reals
Theorem
The ring of integers $\struct {\Z, +, \times}$ forms a subring of the field of real numbers.
Proof
We have that the set of integers $\Z$ are a subset of the real numbers $\R$.
The field of real numbers is, a fortiori, also a ring.
Hence the result, by definition of subring.
$\blacksquare$