Let $S$ Be the Set of All Strings in 0 'S and 'S

Let $S$ be the set of all strings in 0 's and 1's, and define a function $g : S \longrightarrow \mathbf { Z }$ as follows: for each string $s$ in $S$ ,
$$g ( s ) = \text { the number of } 0 \text { 's in } s .$$
(a) What is $g ( 101011 )$ ? $g ( 00100 )$ ?
(b) Is $g$ one-to-one? Prove or give a counterexample.
(c) Is $g$ onto? Prove or give a counterexample.