Why copy constructor argument should be const in C++?

Answer:

There are some important reasons to use const in the copy constructor.

• const keyword avoids accidental changes.
• You would like to be able to create a copy of the const objects. But if you’re not passing your argument with a const qualifier, then you can’t create copies of const objects.
• You couldn’t create copies from temporary reference, because temporary objects are rvalue, and can’t be bound to reference to non-const.