Chapter 25
Raw Arrays, and Why vector Exists
No size, no bounds checking, and the moment an array stops being one.
Part 2
This chapter needs a key
Chapter 24 showed you text without std::string. This is numbers without std::vector, which is where you find out what push_back and .size() were actually protecting you from.
You'll build: Write past the end and find out. Clobber a neighbour, lose an array's size in a function call, and read what survives.
Part 1, chapters 0 to 21, is free and always will be.