First parameter is passed by reference

Inclusion of the & in front of the parameter name in the formal parameter list specifies that the first parameter named x will be passed to the function by reference.

Second parameter is passed by value

The absence of a similar & with the second parameter specifies that the second parameter named y will be passed by value as before.

Otherwise identical

Otherwise, the code in the function named aFunction and the code in the function named main is exactly the same as in the program discussed earlier in conjunction with Listing 3.