In each of the following examples determine the number of homomorphisms between the given groups:
$(a)$ from $\mathbb{Z}$ to $\mathbb{Z}_{10}$;
$(b)$ from $\mathbb{Z}_{10}$ to $\mathbb{Z}_{10}$;
$(c)$ from $\mathbb{Z}_{8}$ to $\mathbb{Z}_{10}$.
Could anyone just give me hints for the problem? Well, let $f:\mathbb{Z}\rightarrow \mathbb{Z}_{10}$ be homo, then $f(1)=[n]$ for any $[n]\in \mathbb{Z}_{10}$ will give a homomorphism hence there are $10$ for (a)?