How can you change values in call by reference?

Answer 1

We don't call by reference, we call functions. The arguments passed to the function are passed (not called) either by value or by reference, depending upon the function signature (the prototype).

When you pass by reference you are passing the actual variable, not a copy of the variable, thus the function can modify that variable's value directly. The only exception is when the parameter is declared a constant reference.

Passing a pointer is essentially the same as passing by reference, however the pointer itself is passed by value. To pass a pointer by reference you must pass a pointer-to-pointer instead.

Passing by value always copies the value, whether it is declared constant or not. But if it is declared constant, the function might as well accept a constant reference. Passing objects (instances of a class) by constant value will incur a performance penalty in making an unnecessary copy. If it is constant, there is little point in copying the object.