Difference between call by address and call by reference

Answer 1

int &x = variable is a direct reference to the address of variable
int *x = &variable is a pointer to a reference of a variable.
here are some differences from stack overflow
-A pointer can be re-assigned any number of times while a reference cannot be re-seated after binding.
-Pointers can point nowhere (NULL), whereas reference always refer to an object.
-You can't take the address of a reference like you can with pointers.
-There's no "reference arithmetics" (but you can take the address of an object pointed by a reference and do pointer arithmetics on it as in &obj + 5)

there are other syntax differences that you should know like when referencing a class you can access it like normal e.g. x.value but with a pointer you have to do x->value or (*x).value to access it.

Answer 2

you mean a pointer and a reference? if i understand it correctly there is no difference between what youre asking.

Answer 3

int Sum(int *x) and int Sum(int &x)