How to show that the circle group T is isomorphic to $\mathbb R/ \mathbb Z$

the circle group is the multiplicative group of all complex numbers of absolute value 1. How can i show that this group is isomorphic with $\mathbb R/ \mathbb Z$. Any hints for the right map is great.

Solutions Collecting From Web of "How to show that the circle group T is isomorphic to $\mathbb R/ \mathbb Z$"