C pointer arithmetic

Question

Given this code:

int *p, *q;

p = (int *) 1000;
q = (int *) 2000;

What is q - p and how?

Answer 1

q - p is 250.

2000 - 1000 = 1000
1000 / sizeof(int) = 250

pointer arithmetic, assuming sizeof(int) is 4.

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Edit: OK, to clarify. In C when two pointers are of the same type then the difference between them is defined the number of things of the pointed-to type between them. For example,

struct foo { int ar[1000]; } big[10];
char small[10];

struct foo *fs, *fe;
char *ss, *se;

fs = &big[0]; fe = &big[9];
ss = &small[0]; se = &small[9];

fe - fs == se - ss;

That is, the difference between the two pointers in this case is the number of array elements between them. In this case it is 0, 1, ... 8 or 9 elements.