const and pointers

void main()
{
    double d = 3.5;
    const double CD = 4.5;
    double* ptr;          // pointer to double
    double const* ptr2cd; // pointer to const double
    ptr = &d;             // OK
    ptr = &CD; // Error: address of const can't be assigned to non-const pointer
    ptr2cd = &d;          // OK
    ptr2cd = &CD;         // OK
}