Question

typedef struct stack{
 int size;
 int array[30];
}STACK;

int p;
STACK *W;

What is the difference between (*W).array and (*W).array[0]?
How do I get an int pointer to the first element in the array if I have W and p?

Answer 1

What is the difference between (*W).array and (*W).array[0]

W->array is an array and W->array[0] is an element.

How do I get an int pointer to the first element in the array if I
have W and p?

Don’t know what you want to do with p but W->array already decays to a pointer to the first element. However, if you want, say, the fifth element:

int *p = &W->array[4];