Pointer Arithmetic

int a[] = {1,2,3,4,5};
int *p = &a[1];   // points to a[1]
int *q = &a[4];   // points to a[4]

q - p;   // → 3  (elements, not bytes!)  type: ptrdiff_t
p + 2;   // → &a[3], advances 2×sizeof(int) bytes in memory

// Pointer TO an array (not to an element)
int (*ap)[3] = &a;   // type: int(*)[3]
(*ap)[0];            // → 1: deref first (→ array), then index
ap++;                // advances sizeof(int[3]) = 12 bytes!

*ap[0]   // → *(ap[0]) — [] beats * — DIFFERENT THING!

Type	32-bit	64-bit (Linux)
int	4 bytes	4 bytes
long	4 bytes	8 bytes
pointer	4 bytes	8 bytes
ptrdiff_t	4 bytes	8 bytes
uint32_t	4 bytes	4 bytes — always, use this in embedded!