Integral Domain in Ring

Integral Domain: A commutative ring with unity is said to be an integral domain if it has no zero-divisors. Alternatively a commutative ring R with unity is called an integral domain if for all a,b \in R, ab = 0 \Rightarrow a = 0\,\,\,{\text{or}}\,\,\,b =  0.

(i) The set Iof integers under usual addition and multiplication is an integral domain as for any two integersa,b, ab  = 0 \Rightarrow a = 0\,\,\,{\text{or}}\,\,\,b = 0.
(ii) Consider a ring R = \left\{ {0,1,2,3,4,5,6,7}  \right\} under the addition and multiplication modulo 8. This ring is commutative but it is not integral domain because2 \in R, 4  \in R are two non-zero elements such that 2 \cdot 4 \equiv 0\left( {\bmod 8} \right).
(iii) The ring of complex numbers \mathbb{C} is an integral domain.
Let J\left( i \right) = \left\{ {a + ib:a,b \in I}  \right\}. It is easy to prove that J\left(  i \right) is a commutative ring with unity. The zero element 0 + 0i and unit element 1 + 0i. Also this ring is free from zero-divisor because the product of two non-zero complex numbers cannot be zero. Hence J\left( i \right) is an integral domain.