cppreference.com > C++ Algorithms > adjacent_difference adjacent_difference Syntax:
      #include <algorithm>
      iterator adjacent_difference( iterator start, iterator end, iterator result );
      iterator adjacent_difference( iterator start, iterator end, iterator result, BinaryFunction f );
The adjacent_difference() function calculates the differences between adjacent elements in the range [start,end) and stores the result starting at result. If a binary function f is given, it is used instead of the - operator to compute the differences. adjacent_difference() runs in linear time. Related topics: accumulate count inner_product partial_sum