JuniorTheoryVery common

Which line of this program does not compile?

C++

int main() {
    int a = 1;
    int b = 2;
    const int* p = &a;
    int* const q = &b;
    p = &b;
    *p = 4;
    *q = 3;
    return a + *p;
}

*p = 4;: p cannot change the int it points to

Expecting p = &b; to fail: in const int* p the const belongs to the int, so p itself may point elsewhere.
Expecting *q = 3; to fail: in int* const q the const belongs to the pointer, so the int may change through q.

How would you declare a pointer where neither the pointer itself nor the value it points to can change?
Why does a function that only reads numbers take const int* data rather than int* data?

JuniorTheoryVery common

C++

int main() {
    int a = 1;
    int b = 2;
    const int* p = &a;
    int* const q = &b;
    p = &b;
    *p = 4;
    *q = 3;
    return a + *p;
}

*p = 4;: p cannot change the int it points to

Expecting p = &b; to fail: in const int* p the const belongs to the int, so p itself may point elsewhere.
Expecting *q = 3; to fail: in int* const q the const belongs to the pointer, so the int may change through q.

How would you declare a pointer where neither the pointer itself nor the value it points to can change?
Why does a function that only reads numbers take const int* data rather than int* data?