## adjacent_difference

    Generalized Numeric Operation

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings

### Summary

Outputs a sequence of the differences between each adjacent pair of elements in a range.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

    #include <numeric>
    template <class InputIterator, class OutputIterator>
    OutputIterator adjacent_difference (InputIterator first,
                                        InputIterator last,
                                        OutputIterator result);
    template <class InputIterator,
              class OutputIterator,
              class BinaryOperation>
    OutputIterator adjacent_difference (InputIterator first,
                                        InputIterator last,
                                        OutputIterator result,
                                        BinaryOperation bin_op);

### Description

Informally, adjacent_difference fills a sequence with the differences between successive elements in a container. The result is a sequence in which the first element is equal to the first element of the sequence being processed, and the remaining elements are equal to the calculated differences between adjacent elements. For instance, applying adjacent_difference to {1,2,3,5} produces a result of {1,1,1,2}.

By default, subtraction is used to compute the difference, but you can supply any binary operator. The binary operator is then applied to adjacent elements. For example, by supplying the plus (+) operator, the result of applying adjacent_difference to {1,2,3,5} is the sequence {1,3,5,8}.

Formally, adjacent_difference assigns to every element referred to by iterator `i` in the range `[result + 1, result + (last - first))` a value equal to the appropriate one of the following:

`*(first + (i - result)) - *(first + (i - result) - 1)`

or

    binary_op (*(first + (i - result)),
               *(first + (i - result) - 1))

`result` is assigned the value of `*first`.

`binary_op` should not have side effects.

`adjacent_difference` returns `result + (last - first)`.

`result` can be equal to `first`. This allows you to place the results of applying adjacent_difference into the original sequence.

### Complexity

This algorithm performs exactly `(last-first) - 1` applications of the default operation (`-`) or `binary_op`.

### Example

    //
    // adj_diff.cpp
    //
     #include<numeric>       //For adjacent_difference
     #include<vector>        //For vector
     #include<functional>    //For times
     #include <iostream>
     using namespace std;
     int main()
     {
       //
       //Initialize a vector of ints from an array
       //
       int arr[10] = {1,1,2,3,5,8,13,21,34,55};
       vector<int> v(arr,arr+10);
       //
       //Two uninitialized vectors for storing results
       //
       vector<int> diffs(10), prods(10);
       //
       //Calculate difference(s) using default operator (minus)
       //
       adjacent_difference(v.begin(),v.end(),diffs.begin());
       //
       //Calculate difference(s) using the times operator
       //
       adjacent_difference(v.begin(), v.end(), prods.begin(),
             times<int>());
       //
       //Output the results
       //
       cout << "For the vector: " << endl << "     ";
       copy(v.begin(),v.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl << endl;
       cout << "The differences between adjacent elements are: "
            << endl << "     ";
       copy(diffs.begin(),diffs.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl << endl;
       cout << "The products of adjacent elements are: "
            << endl << "     ";
       copy(prods.begin(),prods.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl;
       return 0;

Program Output

    For the vector:
         1 1 2 3 5 8 13 21 34 55
    The differences between adjacent elements are:
        1 0 1 1 2 3 5 8 13 21
    The products of adjacent elements are:
         1 1 2 6 15 40 104 273 714 1870

### Warnings

If your compiler does not support default template parameters, then you always need to supply the `Allocator` template argument. For instance, you have to write:

    vector<int,allocator<int> >

instead of:

    vector<int>

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998