Pointer Arithmetic Array Walk

Pointers Scale by Type

In C, a pointer is not just an address. When you write ptr++, the CPU advances by sizeof(*ptr) bytes, not by one. An int* on x86-64 moves 4 bytes per increment; a char* moves 1. This is why arr[i] desugars to *(arr + i) and why the Linux kernel walks buffers with pointer comparisons instead of index variables.

Walking an Array Without Indexing

The idiomatic loop uses a start pointer, an end pointer one past the last element, and strict less-than comparison:

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• arr + n points one past the last valid element (valid in C, do not dereference it)
• p < end avoids off-by-one errors that p <= arr+n-1 invites
• Reverse in place swaps from both ends with two pointers walking inward

For this exercise, you will implement sum_array, max_array, reverse_array, and count_occurrences using only *, ++, and pointer comparison. This task asks you to internalize the scaling rule, because every buffer walk in SQLite, glibc, and kernel code is this pattern with a different type size.

Keep the relevant man page, ABI doc, or Rust reference chapter open while you work. When your output disagrees with the reference implementation on the same machine, the mismatch is usually an alignment rule, an off-by-one terminator, or a register slot you misread in GDB.