Explain the different positions of const with pointers.

The position of const relative to * determines what is read-only. Read declarations right-to-left:

const int *p;       // pointer to const int — can't modify *p, can reassign p
int * const p;      // const pointer to int — can modify *p, can't reassign p
const int * const p;// const pointer to const int — can't modify either

In embedded systems, const int * is used for function parameters to promise the function won't modify the caller's data. int * const is used for memory-mapped register pointers that always point to the same address. const also helps the compiler place data in flash (.rodata) instead of RAM, saving precious RAM on small MCUs.