What the difference between call by reference and call by value return in c plus plus?

In a pass by pointer (*, the original C standard), you're not passing the actual variable but rather its address in memory. This is required because in standard C, all function parameters are passed by value and therefore disappear when the function call is completed. In order to access and alter the original variable, you have to dereference the pointer using the address provided in the pointer argument, and this must be done each time the original variable is altered. Keeping this in mind requires vigilance to be sure you know which object referring: the variable or its memory address.

In a pass by reference (&, introduced in C++), you're telling the compiler that the variable being passed into a function has to be fundamentally linked to the original. The compiler takes care of the dirty work and lets you refer to the variable with simple assignment statements--no pointer handling required.