The program output

The output produced by the program is shown below:

In main
a = 10 b = 20.1
In aFunction
x = 10 y = 20.1
Change x and y
Still in aFunction
x = 100 y = 200.1
Back in main
a = 100 b = 20.1

The important difference

The important difference between this output and the output produced by the previous program is highlighted in boldface. 

Changing the value of a parameter that was passed by reference changes the value stored in the variable that was passed by reference.