character input for an integer variable?
A0 and A1 are not characters or what you mean probably: strings.
Because it would be written as "A0" and "A1".
The types of A0 and A1 are probably integers or another numeric type.

However, these are probably defined as (constant) integers, e.g.:

const int A0 = 100;
const int A1 = 101;


(note 100 and 101 are random numbers)

or defined by a macro. e.g.:

#define A0  100
#define A1  101


So the variables A0 and A1 are actually integers (or assigned as numeric values by a define).