Which of the following assignments would be a compilation error? Assigning the address of a derived-class object to a base-class pointer. Assigning the address of a base-class object to a base-class pointer. Assigning the address of a derived-class object to a derived-class pointer. Assigning the address of a base-class object to a derived-class pointer.

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1. Let the base class be $$ \text{Base} $$ and the derived class be $$ \text{Derived} $$, which is formally declared as:
   $$
   \text{class Derived : public Base \{ ... \};}
   $$

2. **Assigning the address of a derived-class object to a base-class pointer:**  
   This is allowed (upcasting). For example:
   $$
   \text{Base* p = new Derived();}
   $$

3. **Assigning the address of a base-class object to a base-class pointer:**  
   This is allowed since the pointer's type matches the object's type. For example:
   $$
   \text{Base* p = new Base();}
   $$

4. **Assigning the address of a derived-class object to a derived-class pointer:**  
   This is allowed because both the pointer and object's types match. For example:
   $$
   \text{Derived* p = new Derived();}
   $$

5. **Assigning the address of a base-class object to a derived-class pointer:**  
   This is not allowed (downcasting) because the base object does not have the properties of the derived class. For example:
   $$
   \text{Derived* p = new Base(); // Compilation error}
   $$

Thus, the assignment that would result in a compilation error is:

$$
\text{Assigning the address of a base-class object to a derived-class pointer.}
$$
Assigning the address of a base-class object to a derived-class pointer would cause a compilation error.

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