In C++, encapsulation and abstraction in multi-level inheritance are primarily enforced using private and protected access specifiers. While private members are inaccessible outside the class, protected members can be accessed by derived classes, ensuring a controlled inheritance mechanism.

A for loop is best suited when the number of iterations is known ahead of time, as it allows for an initial statement (typically for initialization), a condition check, and an increment/decrement operation in a compact syntax.

The STL vector maintains its elements in a contiguous block of memory. Inserting or erasing elements in the middle requires shifting elements, which can be expensive, especially for large datasets. This might cause frequent reallocations and data movements, impacting performance.

A friend function, although not a member of a class, can access its private and protected members. This provides an external function the capability to interact closely with the internals of the class.

The getline function is used in C++ to read an entire line from an input stream, such as a file. This is particularly useful when dealing with strings that have spaces or when reading full sentences.

A friend class in C++ is a class that is given permission to access the private and protected members of another class. To declare a class as a friend of another class, the friend keyword is used before the class declaration in the original class.

The C++98 standard was officially published in 1998. It was the first standardized version of the C++ language, providing a foundation for many modern C++ features and establishing a baseline for future improvements.

Deleting a memory location more than once leads to undefined behavior, most commonly resulting in program crashes. Always ensure memory is deleted once and pointers are set to nullptr afterwards.

The "void" return type specifies that a function doesn't return a value. It's used when the primary purpose of the function is to perform an action, not produce data.

The bitwise NOT operator (~) inverts each bit of a number. If the bit is 0, it becomes 1, and if it's 1, it becomes 0. This is essentially a negation operation on individual bits.

Using a truth table can help in analyzing and simplifying complex conditions. By representing all possible input combinations and their results, a truth table provides a clear view of the logic, helping in both implementation and debugging of if-else structures.

The base case of a recursive function provides the termination criteria for the recursion. Without a base case, the recursive calls would go on indefinitely, leading to a stack overflow. The base case typically provides a straightforward solution without the need for further recursion.