Another way to pass an argument by reference is to use a pointer variable as the parameter in function. It is still easier to work with reference variable than the pointer but it is necessary to use pointer variable as a function because some C++ library has many functions that uses pointer as parameters. Also when dealing with strings, pointers is useful. Pointers to Constants: A pointer to constant points to a constant item. The data that the pointer points to cannot change, but the pointer itself can change.