Final answer:
The prototype of function f() would be void f(int **ptr). When a double pointer to an integer is passed to the function, it allows for the modification of the original pointer variable or assignment of a new memory address.
Step-by-step explanation:
The prototype of function f() would be void f(int **ptr). This means that the function f() takes a double pointer to an integer as its argument.
In C, a pointer is a variable that stores the memory address of another variable. In this case, the int *p is a pointer to an integer, and &p is the address of that pointer. Passing &p to f() means that the function will receive a pointer to a pointer to an integer.
By receiving a double pointer as an argument, function f() can modify the value of the original pointer *p or even assign a new memory address to it if needed. This can be useful when you want to change the value of a pointer variable within a function.