Tail recursion optimization, often referred to as Tail Call Optimization (TCO), primarily serves to improve memory efficiency. When a recursive call is the last thing a function does (tail recursion), some languages can optimize it to reuse the current function's stack frame for the next function call. This can lead to significant savings in stack space, especially for deep recursive calls. It allows recursion-intensive algorithms to run without consuming as much memory or leading to a stack overflow.

The "&" (ampersand) operator is used to get the memory address of a variable in C++. For instance, if int x = 10;, then &x will give the memory address where the integer x is stored. The asterisk (*), on the other hand, is used for dereferencing.

Both struct and class in C++ can have member functions, data members, and can support inheritance. The primary difference is the default access level: members of a struct are public by default, whereas members of a class are private. Other functionalities between them are essentially identical.

While erase can remove elements from a vector, to efficiently remove all instances of a value, you'd first use remove to move those elements to the end and then use erase. This is known as the "erase-remove" idiom in C++.

In C++, the "base" keyword is not actually used. The correct way to access base class members is through the use of the base class name or the scope resolution operator. However, "base" is a term from C#.

Encapsulation is a key concept in object-oriented programming where the data (members) and the functions (methods) that operate on this data are bundled together as a single unit known as a class.

The noexcept specifier in C++11 and later indicates that a function does not throw exceptions. If such a function does throw an exception, the program will terminate (usually by calling std::terminate). This can be a useful optimization hint for the compiler.

In C++, the long long int data type is designed to store very large integers. It can typically store at least 64 bits, allowing for a wide range of integer values far beyond the standard int.

In C++11 and newer versions, the range-based for loop provides a more readable syntax to iterate over all elements of a container or an array. The loop automatically gets the begin and end iterators of the range and iterates over each element without needing manual indexing.

In C++, the members of a structure (struct) are public by default. This means they can be accessed from functions outside the structure. This is in contrast to the members of a class, which are private by default and cannot be accessed or viewed outside of the class.