Understanding C++ Pointer Assignments

Explanation:

Given the declarations:

double* dp = new double(3);

void* vp;

int* ip;

The compiler will raise errors for the following assignments:

1. dp = vp; - Cannot assign a `void*` pointer to a specific type without casting.
2. ip = dp; - Cannot directly assign a pointer of type `double*` to `int*` without a cast.
3. dp = ip; - Unable to assign an `int*` pointer to a `double*` pointer without a cast.
4. ip = vp; - Similar to the first case, cannot assign `void*` to `int*` without a cast.

However, the compiler will not complain about:

1. ip = (int*) vp; - This is an explicit C-style cast.
2. ip = reinterpret_cast(dp); - This is a reinterpret cast that forces a bit-by-bit conversion.

The valid C++ style casts are explicit and checked during compile-time, explaining why `static_cast` does not work for casting from one pointer type to an unrelated pointer type.

Regarding the value of *ip, it will not be 3 after any of the assignments mentioned above because the data representation of a `double` and an `int` is different. Thus, *ip will likely hold a nonsensical or undefined value after such a cast.