Distance Between Pointers

Implement range queries with pointer subtraction: ``c /* returns how many elements lie in [lo, hi) of array a (n elements), where lo and hi are pointers INTO a (or hi == a + n). Invalid inputs (NULL, hi < lo, pointers outside the array's [a, a+n] range) return 0. */ size_t span(const int *a, size_t n, const int *lo, const int *hi); ``

Difficulty: intermediate