C++ class help

Question

Hello everyone I was wondering if you can help me out on some questions,
What is a properly defined structure
struct {int a};
struct a_struct {int a;}
struct a_struct int a;
struct a_struct {int a;};
another question is when a class is instantiated is a constructor method always executed? Or method and destructor is always executed and lastly can classes can be istantiated more than once.

Answer 1

Every time when the class is instantiated the constructor is called.

Answer 2

A class can be instantiated as many times as necessary. Except for a class designed with Singleton design.

https://www.sololearn.com/learn/675/?ref=app

Answer 3

The properly defined structure is - struct a_struct{Int a;};

Answer 4

A class can be instantiated only once