C - Changing the value of a variable outside of a function by passing pointers

C - Changing the value of a variable outside of a function by passing
pointers

I have an assignment in C to implement a abstract data type STACK. The
nature of the data type requires key structure that needs to have memory
allocated. My problem is that my instructor insists, for now, for the
initialization function to take in a pointer to the key structure. The
init() function will do nothing more than allocate the memory necessary
for the structure and set a field to zero, but the pointer that is passed
in needs to be assigned that memory location.
I can't think of a way to do this without either having the function
return a pointer, or to pass in a 2-star pointer - both of which are not
allowed. I know The function prototype must be (where stackT* is a pointer
to the key STACK data structure):
void init(stackT* stack);
I came up with this and it works fine:
void init(stackT** stack){
*stack = (stackT*) malloc(sizeof(stack));
(*stack)->count = 0;
return;
}
But it does not abide by the restrictions of the assignment.



So basically, how can I pass in the address of my original pointer to the
STACK data structure (&stackPtr) into a function that takes one-star
pointers as arguments and not get a pointer-type warning? Further, once
you change the arguments to (stackT* stack) the below code does not work,
even though I am passing the same thing either way - this is where my
problem is.
I thought it is REQUIRED to have the argument as a 2-star pointer if you
intend to pass in a pointer to a pointer .. the compiler must know what it
is dealing with when you dereference a pointer.
At any rate, I am not sure how to do this given the restrictions. In my
opinion this is only making it necessarily more difficult.