p2 is not pointing to 'F', it is pointing to 'A' and p1 is pointing to '/0'
now, see difference of pointers gives number of hops b/w them.
since int is of 2 bytes, incrementing int pointer(p2 or p1) by 1, increments them with 2 bytes....
now see p2-p1 will give number of hops b/w two of them which is = 3, but we are doing p2-p1(p2 is at lower address), so put negative sign
finally p2-p1 = -3