std::accumulate

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Defined in header `<numeric>`

template< class InputIterator, class T > T accumulate( InputIterator first, InputIterator last, T init );	(1)

template< class InputIterator, class T, class BinaryOperation > T accumulate( InputIterator first, InputIterator last, T init, BinaryOperation op );	(2)

Computes the sum of the given value init and the elements in the range [first, last). The first version uses operator+ to sum up the elements, the second version uses the given binary function op.

The signature does not need to have const &.
The type Type1 must be such that an object of type T can be implicitly converted to Type1. The type Type2 must be such that an object of type InputIterator can be dereferenced and then implicitly converted to Type2. The type Ret must be such that an object of type T can be assigned a value of type Ret.

[edit] Return value

The sum of the given value and elements in the given range.

[edit] Equivalent function

First version

template<class InputIterator, class T>
T accumulate(InputIterator first, InputIterator last, T value)
{
    for (; first != last; ++first) {
        value = value + *first;
    }
    return value;
}

Second version

template<class InputIterator, class T, class BinaryOperation>
T accumulate(InputIterator first, InputIterator last, T value, 
             BinaryOperation op)
{
    for (; first != last; ++first) {
        value = op(value, *first);
    }
    return value;
}

[edit] Example

#include <iostream>
#include <vector>
#include <numeric>
#include <string>
 
int multiply(int x, int y)
{
    return x*y;
}
 
std::string magic_function(std::string res, int x)
{
    if (x > 5) {
         res += "b";
    } else {
         res += "s";
    }
    return res;
}
 
int main()
{
    std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
 
    int sum = std::accumulate(v.begin(), v.end(), 0);
    int product = std::accumulate(v.begin(), v.end(), 1, multiply);
    std::string magic = std::accumulate(v.begin(), v.end(), std::string(), 
                                        magic_function);
 
    std::cout << sum << '\n'
              << product << '\n'
              << magic << '\n';
}

Output:

55
3628800
sssssbbbbb

[edit] See also

adjacent_difference

computes the differences between adjacent elements in a range
(function template)

inner_product

computes the inner product of two ranges of elements
(function template)

partial_sum

computes the partial sum of a range of elements
(function template)