Here, we are passing the variables by call by reference. This means that the changes that we will make in the parameter would be reflected in the passed argument.
Here, the first variable passed in the function func1 (i.e., y) points to the address of the variable x.
Similarly, the second variable passed in the function func1 (i.e., x) points to the address of the variable y and the third variable passed in the function func1 (i.e., x) points to the address of the variable z.
So, we have y = y + 4 ⇒ y = 10 + 4 = 14
and z = x + y + z ⇒ z = 14 + 14 + 3 = 31
z will be returned to x. So, x = 31 and y will remain 3.