Searching Algorithms (find, binary_search, lower_bound)

The <algorithm> header gives you two families of search functions: linear scans that work on any sequence, and binary searches that demand a sorted range. Picking the wrong family is one of the most common STL mistakes: calling std::binary_search on an unsorted vector compiles, runs, and silently lies. This chapter walks through both families, the iterator categories they expect, the gotchas around custom comparators, and the classic "I need the position, not a yes/no answer" trap.