411 REFERENCE · Wikibooks
C++ Language/Std/Stl/Algorithms/ApplyingItemByItem/ProcessingItemByItem
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If you have a function like void DoubleEach(int& x) { x *= 2; }, then you can repeatedly apply that same callable-object, once per collection item.
The algorithm to do so is std::for_each(v.begin(), v.end(), DoubleEach).
Additional information about item-by-item processing (includes interactive examples)