Upcast and Downcast?

Question

OOP

Help solve this dilemma forever.
Let's say the following code is written in pseudocode:

class A {

}

class B inherit from A {

}

class Program {
  public static void Main () {
    A first = new A();
    B second = new B();
    B third = new B();
    //1 Upcast or Downcast?
    third = first;
    //2 Upcast or Downcast?
    first = second; 
  }
}

And the question is, what is Upcast and what is Downcast?
On the Internet, even in English-language sources, instead of showing the answer in a specific code, as a rule, they immediately begin to climb into the jungle (although for good, before climbing there, you must first give an understanding of the process under discussion).

Answer 1

Upcast - casting a child type to a parent type in the inheritance hierarchy.
Downcast - casting a parent type to a child type.
Upcast is always safe, because you can prove at the stage of writing the code that it is legal.

Answer 2

https://ru.stackoverflow.com/questions/433314/Read...