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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 f); // (2)

Effects:

std::accumulate performs fold operation using f function on range [first, last) starting with init as accumulator value.

Effectively it’s equivalent of: 

T acc = init;
for (auto it = first; first != last; ++it)
    acc = f(acc, *it);
return acc;

In version (1) operator+ is used in place of f, so accumulate over container is equivalent of sum of container elements.

Parameters:

first, last - the range to apply f to. init - initial value of accumulator. f - binary folding function.

Return value:

Accumulated value of f applications.

Complexity:

O(n×k), where n is the distance from first to last, O(k) is complexity of f function.

Example:

Simple sum example: 

std::vector<int> v { 2, 3, 4 };
auto sum = std::accumulate(v.begin(), v.end(), 1);
std::cout << sum << std::endl;

Output: 

10

Convert digits to number: 

class Converter {
public:
    int operator()(int a, int d) const { return a * 10 + d; }
};

and later 

const int ds[3] = {1, 2, 3};
int n = std::accumulate(ds, ds + 3, 0, Converter());
std::cout << n << std::endl;
const std::vector<int> ds = {1, 2, 3};
int n = std::accumulate(ds.begin(), ds.end(),
                        0,
                        [](int a, int d) { return a * 10 + d; });
std::cout << n << std::endl;

Output: 

123
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Standard library algorithms:
* Standard Library Algorithms
* std next permutation
* std for each
* std accumulate
* std find
* std count
* std count if
* std find if
* std min element
* Using std nth element To Find The Median Or Other Quantiles
Table Of Contents
0 Getting started
1 Literals
2 Basic type keywords
3 Operator precedence
4 Floating point arithmetic
5 Bit operators
6 Bit manipulation
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10 const keyword
11 Loops
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17 Pointers
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22 std::atomic
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29 std::any
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31 std::optional
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33 std::function
34 std::forward_list
35 std::iomanip
36 Iterators
37 Basic I/O
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42 Returning multiple values from a function
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91 Date and time with std::chrono
92 Trailing return type
93 Function template overloading
94 Common compile linker errors
95 Design patterns
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98 Type traits
99 One definition rule
100 Unspecified behavio
101 Argument dependent name lookup
102 Attributes
103 Internationalization
104 Profiling
105 Return type covariance
106 Non-static member functions
107 Recursion
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110 C++ vs. C++ 11 vs C++ 17
111 Inline functions
112 Client server examples
113 Header files
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119 C++ 11 memory model
120 Build systems
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122 Type inference
123 Resource management
124 Storage class specifiers
125 Alignment
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127 Linkage specifications
128 Curiusly recurring template pattern
129 Using declaration
130 Typedef and type aliases
131 Layout of object types
132 C incompatibilities
133 Optimization
134 Semaphore
135 Thread synchronization
136 Debugging
137 Futures and promises
138 More undefined behaviors
139 Mutexes
140 Recursive mutex
141 Unit testing
142 decltype
143 Digit separators
144 C++ Containers
145 Arithmetic meta-programming
146 Contributors