Walk, Don't Index

Implement two sums over an int array using ONLY pointer arithmetic — no [ ] indexing anywhere in your implementation: ``c long long sum_walk(const int *a, size_t n); /* forward walk */ long long sum_reverse(const int *a, size_t n); /* walk from one-past-end backwards */ ` Both return 0 for NULL or n == 0. Use (a + n)` as the one-past-the-end pointer.

Difficulty: intermediate