C++ POOL — DAY 16

Stop rewriting everything: discovering the standard library containers.

After two weeks implementing lists, stacks and trees by hand, the day reveals that C++ provides all of it, tested and optimised. The point is no longer writing those structures but choosing the right one: each has its strengths and its costs, and picking the wrong container is a performance mistake you only see in production.

Two standard containers put to work: an std::vector of member function pointers for a koala that learns and forgets commands, and two std::stack instances to evaluate an arithmetic expression.