Syntax Fundamentals & Data Structures Flashcards

What is the output of the following code? ```cpp int x = 5; std::cout << x++ << " " << ++x; ```

Answer: 5 7

x++ returns 5 (post-increment), then ++x increments to 7 and returns 7, giving '5 7'.

Which container provides O(1) average-case lookup by key in C++ STL?

Answer: std::unordered_map

std::unordered_map uses a hash table, giving O(1) average-case lookup, unlike std::map which is O(log n).

What does the following declaration create? ```cpp int* const ptr = &x; ```

Answer: A constant pointer to an integer

int* const ptr declares a constant pointer (the pointer itself cannot be reassigned) to a non-const integer.

Which C++ standard introduced the range-based for loop?

Answer: C++11

The range-based for loop (for (auto x : container)) was introduced in C++11.

What is the size of an empty class in C++?

Answer: 1 byte

C++ guarantees that every object has a unique address, so an empty class has size 1 byte.

Which of the following correctly initializes a std::vector with five zeros?

Answer: std::vector v(5);

std::vector v(5) constructs a vector of 5 elements, all value-initialized to 0.

What is the difference between 'struct' and 'class' in C++?

Answer: struct members are public by default; class members are private by default

The only default difference is access: struct defaults to public, class defaults to private for both members and inheritance.